The Ovule Number Variation Provides New Insights into Taxa Delimitation in Willows (Salix subgen. Salix; Salicaceae)
1
Russian Park of Water Gardens, Polevaya Str., 12, Klyazma mkr, 141230 Pushkino, Russia
2
Department of Plant Science and Landscape Architecture, University of Connecticut, 1376 Storrs Rd., Storrs, CT 06269, USA
*
Author to whom correspondence should be addressed.
Plants 2023, 12(3), 497; https://doi.org/10.3390/plants12030497
Submission received: 16 November 2022
/
Revised: 13 January 2023
/
Accepted: 16 January 2023
/
Published: 21 January 2023
(This article belongs to the Special Issue Taxonomy and Plant Conservation, Volume II)
Abstract
:Salix babylonica, S. alba and S. fragilis are closely related species characterized by the lanceolate, acuminate and serrulate leaves. The boundaries between them are defined by relatively few diagnostic characters, and their identification is not fully solved. Recent studies have demonstrated that the number of ovules present in the ovaries of the willow flower can assist in the identification of the species. The detailed ovule data, characteristic for flowers of each species, S. babylonica, S. alba and S. fragilis, and variation in the number of ovules per ovary were documented using many representatives of these species from various geographic regions. The data included the minimum and maximum number of ovules per valve and per ovary and the percentages of valves with a specific number of ovules in a catkin. Some intermediate genotypes and clusters with similar ovule indexes were observed. The important character for the identification of S. babylonica was the presence of valves with 1 or 2 ovules in the ovaries; S. fragilis had valves with 3 ovules while S. alba had the greater number (4–12).
1. Introduction
The genus Salix, which comprises approximately 450 species of trees and shrubs, represents a group of considerable taxonomic complexity for several reasons. Considerable individual variability and polymorphism along with phenotypic variability during different developmental stages and habitat conditions limit the diagnostic value of many characters [1,2]. The dioecy excludes the full range of reproductive structures important for identification of an individual plant while the nonconcurrent phenology limits observation of generative and vegetative structures at the same time. In addition, natural tendencies toward hybridization, introgression and allopolyploidy complicate the taxonomy of willows.
Traditionally, willow identification was based on morphological characteristics. Later, cytological, genetic, chemical and ecological distinctions were used to differentiate the species [2]. This was followed by extensive studies in molecular biology, which became helpful in defining species limits [3,4]. Most recent investigations have demonstrated that the number of ovules present in the ovaries of the willow flower can be used to confirm the identification of species and hybrids and, in conjunction with traditional morphological and modern molecular techniques, presents additional evidence to support taxonomic decisions [5].
Salix babylonica L. from the section Subalbae, S. alba L. and S. fragilis L. from the section Salix according to Skvortsov [1] are closely related species characterized by the lanceolate, acuminate and serrulate leaves. All three species belong to the subgenus Salix and are morphologically similar [1]. Skvortsov and Golisheva [6] also described similarities in the leaf anatomy of these three species. According to Fang at al. [7], these three species belong to the section Salix.
Salix babylonica is a tree 15–18 m in height and up to 80 cm in trunk diameter with a broad spreading crown, slender pendulous or upright branches. The exact limits of the natural range of S. babylonica are not known. According to Fang at al. [7], it is widespread throughout China, or, according to Skvortsov [1], it is distributed along river valleys in arid and semiarid regions of central and northern China. Salix babylonica is common in cultivation around the world. The northern limit of its successful cultivation in Eurasia is sympatric with the northern margin of commercial peach production, which includes southern England, Belgium, southern Germany, the Czech Republic, Hungary, southern Romania, the Crimea, Caucasus, Uzbekistan, lowlands of Kyrgyzstan, north-east China and the Korean Peninsula [1]. There are many selections and hybrids of S. babylonica and many names associated with them. The taxonomy and application of these names have been confusing [8].
Salix alba (white willow) and S. fragilis (crack willow) are common Eurasian tree species with natural distributions throughout Europe and western and central Asia [1]. Both species belong to the section Salix and are morphologically similar, but the delimitation of these species is evident from genetic studies [9,10,11,12,13]. A few studies published the lists of morphological characters useful for distinguishing between S. alba and S. fragilis, including the most comprehensive treatment by Skvortsov [14]. Still, the boundaries between these species are defined by relatively few diagnostic characters. (The authors continue to use S. fragilis as the name for a glabrous crack willow [15] following Skvortsov [1,14]).
Generally, S. alba is described as having pubescent stems, leaves and buds while S. fragilis is a glabrous willow. However, the degree of the pubescence of S. alba varies greatly. “The problem of the identification of pure and hybrid S. alba and S. fragilis entities is one of the critical matters of systematics of this genus” [16]. Many molecular studies were conducted to clarify definitions of these species [10,11,12,13,16,17,18,19,20,21]. Some of them showed high genetic similarity and suggested a shared ancestry for S. alba and S. fragilis [12,16,22].
Ovule number constitutes an important taxonomic character for distinguishing between various taxonomic groups. The ovule number is a basic trait that determines the potential fertility of plants with more ovules producing a greater proportion of seeds, thus affecting reproductive success [23,24,25]. The ovule number presents a technological advancement and confers some advantage over the traditional morphological characters. While most of the morphological traits are descriptive with a continuous variation without having a clear diagnostic value, the ovule number has a defined numerical range, is stable and is consistent for the species of Salix. Moreover, the ovule count method has a high-resolution power and can indicate the presence of genomes from other species with minimal morphological expression [2,5,15,26,27,28,29,30]. It was recommended that the ovule numbers should be included in the descriptions of new taxa and further taxonomic studies of willows [5].
Previously, Chmelař [26] and Argus [2] listed the ovule index (min–max values) for S. babylonica as 4–4 and 2–4, respectively. The index 2–4 implied that there were valves with 1 and 2 ovules per valve and the index 4–4 that there were valves only with 2 ovules per valve (a normally developed non-aberrated willow ovary contains two valves). In addition, some information on the ovule number for S. alba and S. fragilis was previously reported. Chmelař [26], Valyagina-Malutina [28] and Argus [2] listed the ovule index for S. alba as 12–16, 6–10 and 8–9, respectively. For S. fragilis, the ovule index was reported as 6–8 by Chmelař [26] and 6–6 by Valyagina-Malutina [28]. Though the ovule ranges were quite different in these reports, especially for S. alba, the common trend was that the ovule number was about 6 for S. fragilis while S. alba had greater values.
No information how these researchers obtained these data was presented. It was not clear how many individuals and from which regions were used to define these ranges. No vouchers were designated in these reports, and thus, corresponding material could not be traced to correlate these findings.
Hence, a study of the ovule number for S. babylonica, S. fragilis and S. alba was conducted. The objectives were to establish the baselines for the ovule number for these three species and to determine the extent of its variations. Many representatives of S. babylonica, S. fragilis and S. alba from various geographic regions were analyzed. This information is important for defining the species limits.
2. Materials and Methods
2.1. Plant Materials
For S. babylonica, thirty specimens were selected based on their names, which had epithets “babylonica” and “matsudana” (Appendix A). For S. alba, S. fragilis and their hybrid, seventy-six specimens, collected in various parts of Europe and Asia, were analyzed (Appendix B). The specimens were selected based on their names, which had epithets “alba” and “fragilis”, “alba × fragilis” and “excelsa”. Mostly, specimens identified by prominent salicologists were included into this study. The study also included two other species with lanceolate acuminate and finely serrated leaves—S. mucronata Thunb. and S. tetrasperma Roxb. (one specimen each).
2.2. Ovule Count
Willow flowers are arranged into catkins. Each pistillate flower consists of a single pistil with an ovary, floral bract, and nectary (or nectaries). The willow fruit, or a capsule, is formed by the fusion of two carpels. Each capsule contains two valves, in which ovules were counted. Either ripe or unripe capsules were used for ovule count. In ripe capsules, the counts were based on the number of funiculi (from both undeveloped ovules and developed seeds) in the valves. When unripe capsules were used, the counts were made by forcibly opening immature ovaries and counting the number of ovules present in the valves.
For each specimen, the fractions of valves with different numbers of ovules and the number of ovules per ovary (min/often and max/often, “often” means >50%) were documented. The ovule indices were recorded as the minimum–maximum range of ovules per ovary in a catkin (for example, n = 10–12) [5,29,30]. These data resulted in the detailed characterization of the ovule distribution and efficient fingerprinting of the genotypes. The ovule number was integrated with some morphological parameters. The presence of trichomes at bract apex, number of nectaries (1 or 2) and pubescence of the ovary were recorded for S. babylonica. The presence of trichomes at bract apex and their length were included for S. alba and S. fragilis, as these characters were previously used to distinguish these species; according to Skvortsov [14], S. fragilis has long straight trichomes, which extend by 0.8–2.0 mm beyond the bract margin while trichomes in S. alba extend by only 0.2–0.6 mm beyond bract margin.
3. Results
The specimens were sorted based on the ovule ranges and arranged as a continuum of genotypes with gradually increasing ovule indexes, starting with the lowest values. For S. babylonica (Table 1) the specimens were listed in the descending order of valves with 1 ovule, in parallel to the ascending number of valves with 2 ovules. Starting with Specimen 19, plants had also valves with 3 ovules and were listed with increasing percentages of these valves.
For S. alba and S. fragilis, the specimens with 2–6 ovules per valve were arranged in Table 2 and the specimens with 6–12 ovules per valve in Table 3. The specimens with similar ovule indexes were separated by bold horizontal borders in Table 1, Table 2 and Table 3.
3.1. Salix babylonica
The ovule number in S. babylonica represents a continuous variation with following ovule indexes: 2–3, 2–4, 3–4, 4–4, 3–5, 4–5, 4–6, 2–6 and 2–8 (Table 1). A few trends were discerned. Almost all specimens, except Specimen 1, had the majority of valves with 2 ovules—the important character for the identification of S. babylonica. Specimen 1 was the only specimen that had most valves with 1 ovule and some valves with 2 ovules. Specimens 2–13 had valves with 1 and 2 ovules. Specimens 14–18 had only valves with 2 ovules. Starting with Specimen 19, there was a progressive increase of valves with 3 ovules/valve, along with the presence of some valves with 1 and 2 ovules. Thus, it was recorded that S. babylonica was characterized by the presence of most valves with 2 ovules with a possibility of the occurrence of some valves with 1 and 3 ovules.
Notably, in Specimens 6 and 11 the ovule indexes were different while the percentages of ovules per valve were the same. This is explained by different ovule distribution: Specimen 6 had an arrangement when both valves had 1 ovule, which resulted in the minimum value of 2 ovules pre ovary in the index 2–4. This arrangement did not occur in Specimen 11, which had no ovaries where both valves had 1 ovule, resulting in the minimum value of 3 (ovule index 3–4).
Starting with Specimen 19, the occurrence of valves with 3 ovules/valve resulted in the increase of the maximum value in the ovule indexes (3–5, 4–5, etc.). A larger fraction of valves with 3 ovules in Specimen 30 and the presence of valves with 4 ovules expanded the ovule index to a broader range of 2–8.
Some clusters with similar ovule indexes were observed.
3.1.1. S. babylonica var. sacramenta Marchenko et Kuzovkina, ined.
Specimen 1 is listed as S. babylonica var. sacramenta, represented by a cultivated plant that differed from other specimens by having most valves (61%) with 1 ovule and the ovule index 2–3. The name S. babylonica var. sacramenta was not validly published. The origin of this taxon was not known as there were confusing reports about its introduction. The plant under this name was introduced to Argentina in 1928, either from Russia through USA [31] or from Switzerland [8]. Ragonese and Alberti [32] noted that this clone was introduced to Argentina as S. babylonica var. sacramenta Hortus from Botanical Garden of the University of Copenhagen, Denmark, where it was in cultivation since 1893 from cuttings received from Moscow. They noted that this plant was apparently never described, and there was no possibility to find bibliographic information about it. Krussmann [33] described S. babylonica ‘Sacramento’ as a relatively little-known clone with a less pronounced weeping habit, open crown and large leaves.
We have studied Salix babylonica L. var. sacramenta cultivated in Argentina. It is a tree with slightly pendulous branchlets (Figure 1). The green-gray bark of branches and branchlets retains its color on the side exposed to the sun. Branchlets consist of a few orders of shoots, which develop during a growing season. The leaves have sharp serration and much broader blades are distinguishable from those in other varieties of S. babylonica (Figure 2). Other important characteristics include small stipules, in the shape of small glands, almost invisible on pubescent stems. The buds are ovoid and flattened, partially pubescent on the upper half. The outermost cataphylls inside the buds are mostly glabrous, with hair only above the midrib and along the margins. Catkins are short and densely flowered. Flower bracts are wide rounded, often with uneven edges. Pistillate flowers are borne on a short stipe; pistils have a short style, often with 1 nectary. The epithet sacramenta derives from the name under which this plant was introduced to Argentina.
There were some similarities between Specimen 1 and Specimens 2–6, which had a greater number of valves with 1 ovule compared to other specimens. While the origin of Specimen 2, representing a cultivated plant, was unknown, Specimens 3–5 were collected by Skvortsov in Yunnan province in southern China, suggesting that it was possible that S. babylonica var. sacramenta also originated from the south of China. Notably, Skvortsov placed Specimens 3–5 into a folder called S. babylonica, though the individual specimens were identified only as “Salix”. These specimens had the unusually thin and short annual branchlets, and it was possible that Skvortsov was uncertain about their identity. A similar branching pattern was observed in S. babylonica var. sacramenta, which resulted from the growth of a few cycles of branchlets during a growing season. At the end of each cycle, the tip of the branchlet ceased growth and died; this event was followed by the development of the nearest to the tip axillary bud, which grew into a new shoot. The new shoot pushed the dead tip aside and continued its growth along the previous axis of the branchlet. This process continued throughout the season resulting in a few orders of branchlets forming long and thin stems.
Specimens 2–6, characterized by the ovule index 2–4, were likely the intermediate genotypes between S. babylonica var. sacramenta and S. babylonica ‘Babylon’. Notably, Skvortsov annotated Specimen 6, stating that it was very similar to his samples from China collected in 1998 (Specimens 3–5), and the data on the ovule number confirmed this.
3.1.2. S. babylonica ‘Babylon’
Specimens 7–10 had the ovule index 3–4 and similar morphological characters. Specimen 10 of S. babylonica ‘Babylon’ was studied by Santamour and McArdle [8] and was confirmed to be the pure species based on the previously conducted chemical analysis.
Salix babylonica ‘Babylon’ is a graceful tree with long pendulous slender branches and brown, often purple on the upper side of branchlets (Figure 3). The outermost cataphylls inside the buds are mostly glabrous with hair only above the midrib and along the margins, which is different from S. babylonica var. matsudana H.Ohashi & Yonek (Figure 4). The cultivar name ‘Babylon’ was proposed by Santamour McArdle [8] for the female clone, which possibly provided the basis for the original species description by Linnaeus. They described it as a highly atypical selection from the species that had been introduced along the ancient trade routes through southwest Asia, to the Near East, and to Europe around 1730.
3.1.3. S. babylonica var. matsudana
This group includes Specimens 11–24, most of which were previously identified as S. matsudana. Historically, the two binominals—S. babylonica vs. S. matsudana—were used interchangeably by various researchers. The ovary pubescence and the number of nectaries were usually used to distinguish these two species. Skvortsov [1] and Argus [2] pointed to the inconsistency of the ovary pubescence. A similar trend was also documented here; while most of the specimens had glabrous ovaries, Specimen 18 had pubescent ovaries, and Specimen 19 had both pubescent and glabrous ovaries. Further, Skvortsov [1] and Argus [2] noted that S. babylonica had one nectary while S. matsudana had two. However, all specimens identified as S. matsudana in Table 1 had one nectary except for S. matsudana ‘Umbraculifera’ (Specimen 23), in which only 30% of the flowers had two nectaries. Moreover, in some specimens, flowers had 2 nectaries at the base of the catkins, and the rest of the flowers had only one nectary (Specimens 19 and 23). The number of nectaries varied not only among different specimens of the same species, but also in different branches or catkins of the same specimens.
However, a consistent character was observed, which can be used to distinguish between these two taxa. In all specimens of S. matsudana, including ’Annularis’ (S. babylonica ’Crispa’), ‘Tortuosa’, and ‘Umbraculifera’, the outermost cataphylls inside the buds had dense and long trichomes; while in the specimens of S. babylonica, the outermost cataphylls were mostly glabrous, with hair only above the midrib and along the margins. The taxonomic importance of this character for species differentiation should be further assessed. Noteworthy, Skvortsov [1] used a similar character—pubescence along the edges of the outermost cataphylls—to differentiate two related species S. pentandra L. and S. pseudopentandra Flod.
Some differences between S. babylonica and S. matsudana were observed in cultivation as well. Generally, cultivars of S. matsudana are drought tolerant and tough plants [34]. Salix babylonica and its cultivars were relatively sensitive to winter cold, had limited frost hardiness, and almost never survived north of the USDA Zone 7 without significant injuries. Salix matsudana and its cultivars were hardier in northern climates and could be grown to at least USDA Zone 4a with winter temperatures at −34 °C to −32 °C [35].
The ovule index of specimens previously identified as S. matsudana was 3–5 and included the ranges of 3–4, 4–4, 3–5, 4–5 and 4–6. Most of the specimens had almost all valves with 2 ovules, a few specimens (19–22) had very few, almost “accidental”, valves with 3 ovules while specimens 23 and 24 had even greater number of valves with 3 ovules.
The recent discussion on the taxonomic position of S. matsudana by Ohashi and Yonekura [36] recognized a new variety S. babylonica var. matsudana (Koidz.) H.Ohashi & Yonek. The following specifications, including the pubescent outermost cataphylls and 3–6 ovules per ovary, as described above, should be added to accurately define S. babylonica var. matsudana.
The three cultivars—‘Annularis’ with leaves curved into rings (Specimen 11), ‘Tortuosa’ with irregularly contorted branches and leaves (Specimen 12–15, 21, 22), and ‘Umbraculifera’ with a dense subglobose crown (Specimen 23 and 24)—appeared to belong to var. matsudana based on the presence of the pubescent cataphylls. Cultivars ‘Annularis’ and ’Tortuosa’ represent the products of ancient Chinese selection according to Skvortsov [1]).
‘Annularis’ was reported to be more cold hardy than S. babylonica, which is in accord with genotypes of S. babylonica var. matsudana.
The specimens of ’Tortuosa’ had the intermittent distribution in Table 1; there were specimens with 1 and 2 ovules per valve (Specimens 12 and 13); with only 2 (Specimens 14 and 15); with 1, 2, and 3 (Specimen 21); and with 2 and 3 (Specimen 22) ovules per valve, though the greater majority of valves with 2 ovules and 4–4 index were observed. There were noticeably fewer valves with 1 ovule compared with S. babylonica. ‘Tortuosa’ is characterized by the ovule index 3–5; most ovaries were with 4 ovules.
Specimens 23 and 24 identified as S. matsudana ‘Umbraculifera’ had no valves with 1 ovule, and a much larger (19–24%) proportion of valves with 3 ovules. While the pure S. babylonica is defined by the prevalence of the valves with 2 ovules, the occurrence of a larger number of valves with 3 ovules indicates its relation to S. fragilis (the pure S. fragilis has all valves with 3 ovules). Noteworthy, the shape of the crown of S. matsudana ‘Umbraculifera’, which resemble S. fragilis ‘Bullata’, enabled confidently distinguish this plant (Figure 5). Blackening buds in S. matsudana ‘Umbraculifera’, was another distinguishing character indicating its close relationship with S. fragilis.
The color of thin branches and branchlets of ‘Umbraculifera’ ranges from yellow-greenish to purple-brownish (the upper side of the branches exposed to the sun gets tanned, gaining purple color). Mature branches and leaves are glabrous. Buds blunt at the apex (S. fragilis ‘Bullata’ has acuminate buds). Outermost cataphylls inside the buds densely pubescent as in S. babylonica var. matsudana (glabrous S. fragilis ‘Bullata’) (Figure 5). Young leaves are reddish; unfolding leaves are densely pubescent on the upper side, rarely on the lower side and mainly along the central vein. Stipules are large, with rolled up edges and sparse hairs. Stipule attachment point, as in S. fragilis ‘Bullata’, is on the side of the lower third part of the stipule (in S. babylonica var. babylon—at the base) (Figure 6). Bracts glabrous is acuminate. Ovaries sessile with a very short stipe. Nectary occurred as one or rarely two.
Based on the morphological characters and ovule number, this taxon could be a hybrid of S. babylonica var. matsudana (3–5 ovules/ovary) and S. fragilis ‘Bullata’ (6–6 ovules/ovary). Such a hybrid would have the predicted ovule index of 4–6. However, it is more sensible to rather consider this plant as the intermediate genotype between S. babylonica var. matsudana and S. fragilis.
As evident from the labels, Specimen 24 collected in 1984 at Arnold Arboretum was procured from Morton Arboretum in 1960, and thus it likely represented the same clone as Specimen 23, the catkins from a live specimen from Morton Arboretum, which were procured in 2017. Thus, Specimens 23 and 24 collected 33 years apart had very similar ovule counts: 85% and 78% of valves with 2 ovules, 15% and 22% of valves with 3 ovules, correspondingly, and ovary index 4–6. The small differences in the percentages of valves between two specimens, representing the same clone but grown under different conditions and collected at a large time interval, indicated the stability of this trait.
Specimen 25 collected and identified as S. babylonica by the Swedish researcher S.J. Enander in 1913 in Transbaikalia, north of China, had a large proportion (20%) of valves with 3 ovules. Its identification needs clarification as its leaves were similar to S. fragilis but the crown shape was not evident from the herbarium specimens. This specimen was notable due to its northern occurrence, which is unusual for S. babylonica.
Specimens 27 and 28 from the north of China were less weeping as was evident from the herbarium specimens. Specimens 27 was cited by Skvortsov [1]; p.121 as a remarkable specimen representing a tree up to 20 m tall and more than 1.75 m in diameter found in the oases of A-la Shan (Ho-lan Shan) in 1909 by S. Chetyrkin. These specimens had no valves with 1 ovule and a few valves with 3 ovules.
3.1.4. S. babylonica-fragilis—Group (The Groups Were Originally Designated as Varieties by A.M.; such Designations Were not in Accord with the ICBN and Were Replaced with the Non-Nomenclatural Designations Such as Groups
Specimen 29, previously identified as S. fragilis by Skvortsov, had a few valves (10%) with 1 ovule, most (61%) with 2 ovules, and some (29%) with 3 ovules. While the presence of valves with 1 and 2 ovules is typical for S. babylonica, the greater presence of valves with 3 ovules, typical for S. fragilis, indicated greater involvement of that species. The S. babylonica-fragilis—group is characterized by the ovule index 2–6. It has valves with 1, 2, and 3 ovules with most valves with 2 ovules.
3.1.5. S. babylonica-alba—Group
Specimen 30, which had very few valves (3%) with 1 ovule, some (24%) with 2 ovules, most (56%) with 3 ovules, and some (17%) with 4 ovules was placed at the end of Table 1. While the presence of valves with 1 and 2 ovules connects this specimen to S. babylonica, the presence of valves with 3 ovules indicates the involvement of S. fragilis while the presence of valves with 4 ovules indicates the involvement of S. alba. Thus, this specimen is considered to be the intermediate genotype (Table 2). The S. babylonica-alba—group has ovule index 2–8 and valves with 1, 2, 3, and 4 ovules.
3.1.6. Salix babylonica dolorosa
Another obscure taxon “S. babylonica dolorosa” was analyzed to clarify its affiliation. Santamour and McArdle [8] mentioned that the name “dolorosa” was used variously as S. dolorosa Hort., or in the synonymy with S. babylonica, or as a variety S. babylonica dolorosa Hort. Salix babylonica var. dolorosa Rowen ex Rowlee was suggested to be a variety of the species by Bailey [37]. It was listed as a plant with leaves glaucous underneath, with the common name Wisconsin weeping willow, with a note that this plant is hardy farther north. Bailey [38] referred to it as a synonym of S. blanda, a suggested hybrid of S. babylonica and S. fragilis, and this placement was followed by Rehder [39].
The analysis of the ovule number of the herbarium specimen of S. babylonica var. dolorosa (W.L.G. Edson; 0-711; Highland Park, Rochester, NY, US, collected 8 June 1918, A) indicated the following: 1% of valves with 2 ovules, 88% of valves with 3 ovules, 10% of valves with 4 ovules, and 1% of valves with 5 ovules based on the analysis of 64 ovaries. Its ovule index was 5–8, and a very similar distribution of valves with various ovule number corresponded to S. ×pendulina Wender.
The ovule number in S. alba, S. fragilis, or S. alba × S. fragilis is presented in Table 2 and Table 3. All specimens had various proportions of valves with a different number of ovules. At the beginning of Table 2 the specimens were listed in descending order of valves with 2 ovules, in parallel to the ascending number of valves with 3 ovules. Some of these specimens also had small fractions of valves with 4 or 5 ovules. A gradual transition toward the specimens with greater than 3 ovule per valve was observed toward the end of Table 2 and throughout Table 3. In parallel to the increasing number of ovules per valve, the ovule indexes were also gradually increasing from 4–6 to 20–24. The two groups were distinguishable.
3.2. S. fragilis
Specimens 1–32 had most valves with 3 ovules (Table 2). The ovule indices varied from 4–6 to 6–9 and included the intermediate ranges of 4–7, 4–9, 5–6, 6–6, 5–8, 6–7, and 6–8. The distribution of valves with various ovule number varied among specimens.
3.2.1. S. fragilis-babylonica—Group
Specimens 1–5 had most valves with 3 ovules, typical for S. fragilis, and few valves with 2 ovules, typical for S. babylonica. This subset with the characteristic ovule index of 4–6 was recognized as the intermediate between S. fragilis and S. babylonica and designated as the S. fragilis-babylonica—group, characterized by the ovule index 4–6. It has valves with 2 and 3 ovules with most valves with 3 ovules.
The analysis of the ovule number in S. babylonica described above also identified some specimens as the intermediate variants from S. babylonica to S. fragilis. Those specimens designated as belonging to the S. babylonica-fragilis—group had greater involvement of S. babylonica, as was evidenced by most valves with 1 or 2 ovules, along with some valves with 3 ovules, and the characteristic ovule index 2–6.
3.2.2. The Pure S. fragilis
Specimen 6 had ovule index 6–6, which means that all valves in the ovaries of catkins had 3 ovules. The previously documented ovule index for the pure S. fragilis, which was obtained through the study of the specimens collected in natural areas [15,28] and predicted through the analysis of its hybrids [29], was 6–6. Notably, Specimen 6 was the only specimen that matched the previously reported ovule index for the pure S. fragilis.
3.2.3. S. fragilis-alba—Group
Specimens 7–12 had a small proportion of valves with 2 ovules, most valves with 3 ovules along with some valves with 4 and 5 valves. Specimens 13–22 had most valves with 3 ovules and some valves with 4 ovules, while Specimens 23–32 had also valves with 5 ovules, which are associated with S. alba. This group having most valves with 3 ovules, typical for S. fragilis, was recognized as the intermediate between S. fragilis and S. alba and designated as S. fragilis-alba—group with the ovule index 6–9. It has valves with 3, 4 and 5 ovules with most valves with 3 ovules.
3.3. S. alba
3.3.1. S. alba-fragilis—Group
Starting with Specimen 33 and continuing through Specimen 50, there was a noticeable transition to the genotypes with less than 50% of valves with 3 ovules, in parallel with the greater number of valves with 4 and 5 ovules, typical for S. alba. This group was designated as S. alba-fragilis with the ovule index 6–12 (Table 2). It has valves with 3, 4, 5, and 6 ovules with less than 50% of valves with 3 ovules.
The most common ovule index was 6–10 (a few specimens had the ovule index 7–9, 7–10, 8–10, and 8–11, which were within 6–12 range). The lower value of 6 in this index meant that in these specimens there were some ovaries were both valves had 3 ovules, as in the pure S. fragilis; while the greater upper values in the ovule indexes meant that there were also ovaries with 4, 5, 6 ovules per valve. Specimen 49, previously identified as S. euxina I.V.Belyaeva [40], belongs to this group [15].
3.3.2. The Pure S. alba
Specimens 51–62 had no valves with 3 ovules (associated with S. fragilis), a noticeably higher proportion of valves with 4, 5, and 6 ovules. Specimen 56, first identified by various botanists as pure S. fragilis, was proposed as a new type for that species [41], and later, annotated as the epitype of S. euxina in 2019, belongs to this group [15].
3.3.3. S. alba-excelsa—Group
In Specimens 70–74 the ovule indexes reached the ranges 15–17, 15–18, 16–21, 18–20, and 18–21. This group with high ovule indexes was designated as S. alba-excelsa—group with the ovule index of 15–21 and valves with 7, 8, 9, 10, 11, and 12 ovules (Table 3). This group included specimens previously identified by Skvortsov as S. excelsa J.F.Gmel., a species occurring in Iran, Afghanistan, and Middle Asia, which he considered to be closely-related to S. alba [1]
3.4. Specimen Identifications
When previous identifications of the specimens of S. alba, S. fragilis and their hybrid were checked against the ovule-based data, the variegation in column 1, related to color-coding of the species’ names, was apparent throughout Table 2. Instead of the expected clustering of the specimens belonging to the same species, their scattered distributions indicated the discrepancies between the placement of the specimens in the tables based on the ovule data, and the previous identifications based on the traditional morphologically characters.
Specimens 1–50, which included specimens with 3 ovules per valves appeared to be the most difficult group for identification. Contrary, in almost all specimens without 3 ovules per valve (starting from Specimen 51 in Table 2 and all specimens in Table 3), the ovule number corroborated the specimen identifications as S. alba by different authors. This fact meant that in these specimens there was a strong expression of morphological traits of S. alba, which unambiguously suggested its recognition.
At the other end, all specimens previously identified as S. fragilis (except Specimen 75) had valves with 3 ovules. It is likely that even a small fraction of the valves with 3 ovules, resulted in the expression of the morphological traits typical for S. fragilis. However, in some specimens in the group where most valves had 3 ovules, the presence of valves with a different number of ovules apparently blurred their recognition as S. fragilis.
Notably, in some cases the specimens with similar ovule number were identified interchangeably as different species by the same authors. For example, Specimens 13, 14, 16, 18 had similar proportions of valves with 3 and 4 ovules but were identified either as S. fragilis (Specimens 14 and 18) or as S. alba (Specimens 13 and 16) by Skvortsov, who was often considered to be one of the most experienced researchers of Salix. Based on the ovule number, which included most valves with 3 ovules, all specimens should belong to S. fragilis (S. fragilis-alba—group).
As to the analysis of other morphological characters, many specimens had long bract hair in the S. fragilis-group, fewer in the S. alba-group in the middle of Table 2, and no specimens with long bract hair in the S. alba-group at the end of Table 2 and throughout Table 3. All specimens identified as S. fragilis by Skvortsov had bracts with long trichomes at the apexes. Apparently, Skvortsov considered this character as diagnostic for S. fragilis, though some of these specimens with the long bract hair were not confirmed to be S. fragilis by the ovule number. For example, Specimen 33 and 41, identified by Skvortsov as S. fragilis, had long trichomes at the bract apex, but, based on the presence of the most valves with 4 ovules and ovule indexes 6–10, should rather belong to S. alba.
3.5. Salix tetrasperma and S. mucronata
The ovule number for two other species with lanceolate acuminate and serrulate leaves similar to S. babylonica, S. alba, and S. fragilis—S. tetrasperma (Indian willow) from southern and southeastern Asia and S. mucronata (Cape willow, or safsaf willow) from South Africa were analyzed using the limited number of specimens. Salix tetrasperma had 100% of the valves with 2 ovules (ovule index 4–4, based on the analysis of 52 ovaries from Specimen NA0556465) while S. mucronata had 100% of valves with 6 ovules (ovule index 12–12, based on the analysis of 23 ovaries from Specimen NA0556301). Salix tetrasperma grows in the climatic conditions similar to the conditions of S. babylonica and has the identical ovule index. Salix mucronata, which naturally occurs in harsher climatic conditions and is adapted to colder and drier, had a greater ovule index.
Another species, S. humboldtiana Willd. From the section Humboldtianae, is often cultivated in South America (Argentina and Chile) and Mediterranean region of Europe. S. humboldtiana is also superficially similar to S. babylonica, with which it is occasionally con-fused. However, it is easily distinguishable from S. babylonica by much greater ovule number—20–24 [5].
4. Discussion
The studied specimens of S. babylonica, S. fragilis, or S. alba were from various parts of Europe and Asia, providing a broad geographic context for the ovule variations in these species. While they are closely related species, the boundaries between them are defined by relatively few diagnostic characters, and their identification is still not fully solved as was evidenced by this study. The ovule analyses demonstrated that these species can be distinguished by the ovule number. It was concluded that S. babylonica had most valves with 1 or 2 ovules, S. fragilis with 3 ovules while S. alba had the most valves with the higher number (4, 5, and up to 12) of ovules. In addition, various combinations of the smaller fractions of valves with 3 ovules (typical for S. fragilis) and 4 ovules (typical for S. alba) were recorded in the ovaries of many genotypes of S. babylonica. Some specimens had higher ovule indexes than previously reported (2–4 or 4–4) for S. babylonica—as 3–5, 4–5, 4–6, 2–6, and 2–8.
The occurrence of valves with a larger number of ovules than typical for S. babylonica 1 and 2 ovule/valve indicated the recombination of genomes either through introgression or hybridization. The presence of valves with 3 and 4 ovules indicated the rearrangement of genetic material with some progression to S. fragilis and S. alba. It was possible that the evolution progressed from S. babylonica to a morphologically similar S. alba through the intermediate S. fragilis, the two species which belong to the European–West Asian section Salix.
The studied specimens of S. fragilis had lower levels of variation of the ovule number, ranging from 2 to 5, compared to S. alba, the specimens of which contained a broader range of valves with various ovule number, ranging from 3 to 12.
The specimens which belong to S. fragilis had the majority valves with 3 ovules, and the specimens “S. alba—group” had the majority valves with more than 3 ovules.
When many genotypes of these species were placed in a sequence according to the ovule number, they represented a large continuum of individuals with no clear borders. A gradual transition from S. babylonica to S. fragilis and then to S. alba among studied genotypes was observed as was evidenced by the appearance of valves with larger ovule numbers. The presence of valves with three ovules in certain genotypes of S. babylonica indicated their closeness with S. fragilis while the presence of valves with four or five ovules indicated their closeness with S. alba.
There were many intermediate specimens with various assortments of valves associated with either S. babylonica, S. fragilis or S. alba. The intermediate genotypes of S. babylonica had most valves with 1 or 2 ovules per valve, along with some valves with 3 and 4 ovules. The intermediate genotypes of S. fragilis had most valves with 3 ovules per valve, along with some valves with 2, 4, or 5 ovules. The intermediate genotypes of S. alba had most valves with 4 or more ovules along with some valves with 3 ovules. The presence of the intermediate forms demonstrated that the boundaries between species were not strictly defined, as would not be expected from the nature. It is better to differentiate them as the intermediate taxa rather than hybrids.
Thus, the rearrangement or recombination of valves with various ovule number was recorded, which probably took place during the evolutionary processes in various climatic conditions. A gradual from 1, 2 to 3, and then to 4, 5 and greater number of ovules/valve between closely related species was observed. This change can be interpreted as the transition from S. babylonica to S. alba through S. fragilis (Figure 7), which should be further confirmed by the phylogenetic data.
A notable Specimen 5 was included into Table 1. This specimen from Iran was at first named as S. aegyptiaca by Saberti and later identified as S. babylonica by Skvortsov. It had almost all valves with 3 ovules, a very low number of valves (1%) with 2 ovules, and the ovule index 5–6. The prevalence of valves with 3 ovules indicated that this specimen belongs to S. fragilis but was misidentified by Skvortsov as S. babylonica. This fact points out the morphological similarity of S. babylonica and S. fragilis corroborating a close relationship of these species. Interestingly, S. matsudana Koidz. was distinguished from S. fragilis by Koidzumi [36], which also suggests a close connection between these taxa.
Throughout evolutionary history, plants have developed the reliable reproductive mechanisms insuring their sustained survival across generations. Seed production is a primary means of plant propagation, and the number of ovules correlates to the number of future seeds, which directly affect the survival. Evolutionarily, Salix probably arose in the warm temperate or subtropical regions of eastern Asia [1]. It is possible that the evolution of the number of ovules per ovary has progressed toward its increasing. Salix babylonica var. sacramenta and other specimens from Southern China were probably the most ancient representatives in this group. In the more favorable conditions in the south having one ovule/valve or one seed/valve was sufficient for species survival. In the temperate continental climate, willows also produced a few ovules. The gradual increase of the ovule number could have been observed as species of Salix extended to the north and south from their optimal environments. For example, the pure S. fragilis from Bulgaria has 3 ovules/valve while a larger number of ovules/valve in S. alba had evolutionary advantages in colder climates or in hot and dry environments where the greater number of ovules corresponds to the greater number of potential seeds, which can survive in harsh conditions.
5. Conclusions
The number of ovules present in the ovary of the normally developed willow flower is a stable trait that can be used to confirm species identification when used in combination with morphological and molecular data. The genetic structure of Salix babylonica, S. alba, and S. fragilis appeared to be complex as can be seen from the existence of many individuals with various proportion of valves with a different number of ovules. As more representatives of these species are analyzed in the future, the more adequately their genetic diversity is captured, resulting in more comprehensive understanding of the species delimitations.
Author Contributions
A.M.M. conceptualized the project and analyzed the ovule number and other morphological characters in the specimens; Y.A.K. studied all the materials. Both authors wrote the manuscript. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Data Availability Statement
Data available in a publicly accessible repository at the Center for Open Science’s Open Science Framework (https://osf.io/kdqm5/).
Conflicts of Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Appendix A
Table A1.
Specimen information for S. babylonica used in the present study. The Herbaria where the specimens are kept indicated in bold. The specimen number corresponds to the specimen number in Table 1. The specimen number with asterisk (*) means the live specimens.
Table A1.
Specimen information for S. babylonica used in the present study. The Herbaria where the specimens are kept indicated in bold. The specimen number corresponds to the specimen number in Table 1. The specimen number with asterisk (*) means the live specimens.
| No | Species | Region, Collector, Herbarium |
|---|---|---|
| 1 | S. babylonica var. sacramenta ‘Soveny Americano’ | Argentina, Delta del Parana, Las Carabelas Farm, 29/10/2018; Y.A.Kuzovkina. CONN |
| 2 | S. babylonica | USA, Boston, Arnold Arboretum, cultivated, 05/05/1996. A.K.Skvortsov A.R.Brach. MHA |
| 3 | Salix—specimen No. 1 in the folder “S. babylonica L.” | China, Yunnan Province, Kunming surroundings, foothills, 2000–2500 m. Clonal plantings along the river, 25–28/03/1998. A.K.Skvortsov. MHA |
| 4 | Salix—specimen No. 2 in the folder “S. babylonica L.’ | China, Yunnan province, Kunming surroundings, foothills, 2000–2500 m. Clonal plantings along the river. 25–28/03/1998. MHA |
| 5 | Salix—specimen No. 3 in the folder “S. babylonica L.” | China, Yunnan province, Kunming surroundings, foothills, 2000–2500 m. Clonal plantings along the river, 25–28/03/1998. A.K.Skvortsov. MHA |
| 6 | S. babylonica | NA 46541; USA, Washington, National Arboretum. Collection of willows. Origin unknown. Planted as Salix matsudana ‘Pendula’, collected by F. G. Meyer, 07/05/1987. (Skvortsov’s note: “very simi-lar to my samples from China in 1998”). MHA |
| 7 | S. babylonica | Spain, province of Castellón, Morella; grown in the Botanical Garden of Madrid from cuttings brought from the bank of the Morella River. Collected during the first flowering in the garden. 18/03/1996. P.Blanco, S.Cirujano, R.Morales. MHA |
| 8 * | S. babylonica | Argentina, Patagonia, Neuquen, planted Villa El Chocon; 4/11//2018. Y.A.Kuzovkina. CONN |
| 9 | S. babylonica | Russia, Crimea, Nikitsky Botanical Garden, Collect. I.Artamonova; 03/05/1956. A.K.Skvortsov. MHA |
| 10 | S. babylonica ‘Babylon’ | NA 44011, USA, Washington, National Arboretum. NA |
| 11 | S. babylonica var. annularis | Edson (S. babylonica var. crispa; Loudon) 0–777 Highland Park, Rochester, NY. 6/8/1918. A |
| 12 | S. matsudana f. tortuosa Rehder | No. 360-60-B, USA, Boston, Arnold Arboretum, plot 5-c. Cuttings obtained in 1960 from AA9046 (Western Nursery, Massachusetts, in 1946); D. Michener, E. Bennett, J. Dricker B. Porter; 782; 05/06/1984. MHA |
| 13 * | S. babylonica ‘Tortuosa’ | No. NA 44014, USA, Washington, National Arboretum |
| 14 * | S. matsudana ‘Tortuosa’ | USA, Chicago, Morton Arboretum |
| 15 | S. matsudana var. tortuosa | Czechoslovakia, Moravia, Brno, Dornic. 19/04/1960. Ing. Chmelař. MHA |
| 16 * | S. matsudana | No. 366-79, USA, Chicago, Morton Arboretum |
| 17 | S. matsudana | No. 17177, USA, Boston, Arnold Arboretum, Single-trunk tree 15–16 m high; 160 cm diameter; received from John Vietch Son nursery (England) in 1913 by D. Michener, E. Bennett S. Erwin; 94; 01/05/1984. MHA |
| 18 | S. matsudana f. pendula Schneider | No. 175-61-A, Boston, Arnold Arboretum; map 4-b. Cuttings from Morton’s Arboretum in 1961. S.Elsik, I.Hay, J.Carey, E. Fisch P. Megowen. 771. 04/06/1984. MHA |
| 19 | S. babylonica | Japan, Iwate Prefecture, Usugin, Kawasaki, 02/05/1949. Masao Kikuchi. MHA |
| 20 | S. matsudana | China, Beijing, 1856. Dr. Tatarinow. MHA |
| 21 | S. matsudana var. tortuosa | Spain, Catalonia, Girona: Banyoles, Lake Banyoles. 459813. 04/05/1998. Blanco, Paloma. MHA |
| 22 | S. babylonica ‘Tortuosa’ | USA, Montgomery, Wheaton, Maryland. Japanese Garden, Brookside Gardens, 24/04/1986. F.G.Meyer, P.M. Mazzeo. MHA |
| 23 * | S. matsudana f. umbraculifera | No. 166-82, USA, Chicago, Morton Arboretum |
| 24 | S. matsudana f. umbraculifera | No. 634-60-A, USA, Boston, Arnold Arboretum. Plot 6-b. Origin: from Morton Arboretum in 1960 S.Elsik, I.Hay, J.Carey, E. Fisch P. Megowen. 772. 04/06/1984. MHA |
| 25 | S. babylonica | Transbaikalia, now the microdistrict of Ulan-Ude, Selenga River. 15/07/1913. S.J Enander/A.K. Skvortsov? MHA |
| 26 | S. babylonica | Japan, Honshu, Nagano Prefecture, Matsumoto, Shinshu University Campus 04/04/1976. T. Shimizu. MHA |
| 27 | S. babylonica | China, Alashan, Dyn-yuan-ying oasis; col. S.S.Chetyrkin. 1909. A.K.Skvortsov. MHA |
| 28 | S. babylonica | China, Prov. Liaoning, st. Xunyaochen, 22/05/1950. Lion Tchen-ngo/A.K. Skvortsov? MHA |
| 29 | S. fragilis | Russia, Smolensk region, Kardymovsky district, near Kardymovo village, the bank of the Khmost River. 11/05/1975. A.K.Skvortsov. MHA |
| 30 | S. fragilis | Russia, Smolensk region, okr. Smolensk. Talashkino, along ditch at border of the homestead, probably not planted. 07/05/1975. A.K.Skvortsov. MHA |
Appendix B
Table A2.
Specimen information for S. alba, S. fragilis and S. alba × S. fragilis used in the present study. The Herbaria where the specimens are kept indicated in bold. The specimen number corresponds to the specimen number in Table 1. The specimen number with asterisk (*) means the live specimen.
Table A2.
Specimen information for S. alba, S. fragilis and S. alba × S. fragilis used in the present study. The Herbaria where the specimens are kept indicated in bold. The specimen number corresponds to the specimen number in Table 1. The specimen number with asterisk (*) means the live specimen.
| No | Species | Region, Collector, Herbarium |
|---|---|---|
| 1 | S. fragilis f. latifolia Anderss. | Russia, Mordovia, Saransk. E.T.Malyutina. MHA |
| 2 | S. alba | Portugal, Mertola. P. da Silva, M. Bravo Lima, B. Rainha. MHA |
| 3 | S. alba × S. fragilis | Portugal, Province of Baxio Alentejo, Mertola. P. da Silva, M. Bravo Lima, B. Rainha. MHA |
| 4 | S. alba | Austria, Vienna. A. Neumann. MHA |
| 5 | S. aegyptiaca | Iran, Mazandaran Province: Galanrud, №37175 E. 26/04/1956. Sabeti/S. babylonica L.—A.K.Skvortsov). MHA |
| 6 | S. euxina | 001191972Bulgaria, River Kalnitza, near Botevgrad. 24/04/2015. BM |
| 7 | S. alba | Kazakhstan, Taldy-Kurgan region, r. Karatal, 36–38 km from Ushtobe, the outskirts of the Saryesik-Atyrau desert. A.K.Skvortsov. MHA |
| 8 | S. fragilis | Russia, Mordovia, Saransk. E.T.Malyutina. MHA |
| 9 | S. fragilis | Russia, Moscow region, Serpukhov district, near the village Luzhki. A.K.Skvortsov. MHA |
| 10 | S. fragilis | USSR, Minsk region, Logai district, r. Gaina. A.K.Skvortsov. MHA |
| 11 | S. fragilis var. decipiens | Portugal, Province of Baxio Alentejo. Bento V. Rainha. MHA |
| 12 * | S. alba | Russia, Yekaterinburg, Botanical Garden, salicetum, row 1. I.V.Belyaeva |
| 13 | S. alba | Russia, Moscow region, near Zvenigorod, bank of the river Storozki. A.K.Skvortsov. MHA |
| 14 | S. fragilis | Bohemia, (now Czech Republic), Litomysl. A.K.Skvortsov. MHA |
| 15 | S. alba | Austria, Murau. Gratg/I.V.Belyaeva. K |
| 16 | S. alba | Russia, Stalingrad (now Volgograd) region, near the village Pereshepnoe. A.K.Skvortsov. MHA |
| 17 | S. fragilis | Russia, Ulyanovsk region, Barysh district, s. Rumyantsevo. E.T.Malyutina. MHA |
| 18 | S. fragilis | Russia, Moscow region, Serpukhov district, s. Luzhki. A.K.Skvortsov. MHA |
| 19 | S. alba | Russia, Ulyanovsk region, Barysh district, s. Surskie Vershini. E.T.Malyutina. MHA |
| 20 | S. fragilis L. × S. alba | Russia, Moscow region, the left bank of the Oka below Serpukhov, near s. Luzhki. A.K.Skvortsov. MHA |
| 21 | S. fragilis (×S. alba?) | Russia, Moscow region, right bank of the Oka below Kashira, near the village of Kropotovo. A.K.Skvortsov. MHA |
| 22 | S. alba | Southern Albania. A.H.G.Alston, N.Y. Sandwith/ I.V.Belyaeva. K |
| 23 | S. alba | Russia, Moscow region, Zvenigorod district, Molodenovo village. A.K. Skvortsov. MHA |
| 24 | S. alba | Russia, Moscow region, near Zvenigorod, the bank of the Moscow River. A.K. Skvortsov. MHA |
| 25 | S. alba | Kazakhstan, Taldy-Kurgan region, Ushtobe, the outskirts of the Saryesik-Atyrau desert. A.K. Skvortsov. MHA |
| 26 | S. alba | England, East Yorkshire, Hull, on the road Beverly Road to the village of Newland. C.Waterfall/I.V.Belyaeva. K |
| 27 | S. fragilis × S. alba | Russia, Moscow region, left bank of the Oka below Serpukhov, near the village of Luzhki. A.K.Skvortsov. MHA |
| 28 | S. alba | England, Devon. Drummond/I.V.Belyaeva. K |
| 29 | S. fragilis | Russia, Ulyanovsk region, Gremyachka village. E.T.Malyutina. MHA |
| 30 | S. fragilis | Bulgaria, near the village of Kasitsene, Sofia district. N.Vihodcevsky. MHA |
| 31 | S. alba | Russia, Stalingrad (now Volgograd) region, Kotovsky district, near the village of Popki. A.K.Skvortsov. MHA |
| 32 | S. alba | Russia, Penza region, lake New Sura. E.T.Malyutina. MHA |
| 33 | S. fragilis | Lithuania, outskirts of Kaunas. A.K.Skvortsov. MHA |
| 34 | S. alba var. caerulea | Middlesex, (England), near the water near Longmore. A.B.Jackson/S. alba L.—I.V.Belyaeva. K |
| 35 | S. fragilis | Russia, Orenburg region, Buguruslan district, Kiryushkino village. E.T.Malyutina. MHA |
| 36 | S. alba | Russia, Zap. Altai, Leninogorsk. A.K.Skvortsov. MHA |
| 37 | S. alba | Russia, Saratov region, valley of the river Khoper near Balashov. MHA |
| 38 | S. alba | Russia, Moscow region, Serpukhov district, near the village of Luzhki, floodplain of the Oka. A.K.Skvortsov. MHA |
| 39 | S. fragilis | Russia, Penza region, Kuznetsk district, Tyukhmenevo village. E.T.Malyutina. MHA |
| 40 | S. fragilis | Russia, Penza region, Kuznetsk district, Starye Chasi village. E.T.Malyutina. MHA |
| 41 | S. fragilis | Slovakia, Liptovský Mikuláš district, Parizovice. A.K.Skvortsov? MHA |
| 42 | S. fragilis × S. alba | Russia, Penza region, Kuznetsk district, between the village of Dvoriki and the village of Mordovsky Kachim. E.T.Malyutina. MHA |
| 43 | S. fragilis | USA, Massachusetts, Hampshire, Amherst. H.E.Ahles. MHA |
| 44 | S. alba × S. fragilis | Kazakhstan, Kokchetav region, Shchuchinsk, arboretum KazNIILKH. A.K.Skvortsov. MHA |
| 45 | S. fragilis | Russia, Ulyanovsk region, Inza, on the bank of the Syuksum River. E.T.Malyutina. MHA |
| 46 | S. alba | Russia, Kaluga region, near Tarusa, in the floodplain of the Tarusa River. A.K.Skvortsov. MHA |
| 47 | S. fragilis | Russia, Moscow region, Serpukhov district, near the village of Luzhki. A.K.Skvortsov. MHA |
| 48 | S. fragilis | Russia, Penza region, lake New Sura. E.T.Malyutina. MHA |
| 49 | S. euxina | 001191975 Poland, River Panna, at Tylawa 28/04/2015 BM |
| 50 | S. fragilis | Belgium, Pleinvaux (community of Neupre), (Belgium, province Liège, [bord de l’Qurthe] left bank, not far from Rosiere farm, IFBL/G7.12.22. No. 12931. R. Renard, Vidit J. Lambinon. 11/05/ 1987. MHA |
| 51 | Salix | Greece, North-West Macedonia. A.H.G.Alston, N.Y. Sandwith/S. alba L.—I.V.Belyaeva. K |
| 52 | S. alba | France, Cher, (Centre-Val-de-Loire). I.V.Belyaeva. № 4657. K |
| 53 | Salix | Greece, Macedonia, Lake Kerkini S. alba L.- I.V.Belyaeva. K |
| 54 | Salix | Greece, North-West Macedonia. A.H.G. Alston, N.Y. Sandwith/S. alba L.—I.V.Belyaeva. K |
| 55 | S. alba | Russia, Moscow region, (b. Venevsky Uyezd of Tula Gub.) near the village of Serebryanye Prudy. A.K.Skvortsov. MHA |
| 56 | S. fragilis | 01065618. Turkey, Kars province, near Promezhutochnaya station, bank of the river Kyaklik], 245 ♂ and ♀”. S. Turkevich/S. euxina—I.V.Belyaeva. LE |
| 57 | S. alba | England. Dorling Mills/I.V.Belyaeva. K |
| 58 | S. alba × S. fragilis | Slovakia, Liptovský Mikuláš district. A.K. Skvortsov? MHA |
| 59 | S. alba | Kazakhstan, Taldy-Kurgan region, Karatal river, 36–38 km from Ushtobe, the outskirts of the Saryesik-Atyrau desert. A.K.Skvortsov. MHA |
| 60 | S. alba | Russia, Moscow region, Serpukhov district, Luzhki village. A.K.Skvortsov. MHA |
| 61 | S. alba | Northeast Turkey, A8, Gümüşhane, the valley of the Chorokh River between Maden and Bayburt. A.K.Skvortsov. MHA |
| 62 | S. alba | Greek Macedonia, Struma River near the Kopriva Bridge. M.B. Jurrill/I.V.Belyaeva. K |
| 63 | S. alba var. splendens | Serbia, near Niš (C.K. Schneider/S.×fragilis L. (S. alba × S.euxina I.V.Belyaeva)- I.V.Belyaeva. K |
| 64 | S. alba | England, Hemingford Gray. I.V.Belyaeva. K |
| 65 | S. alba | France, Cher (Centre-Val-de-Loire). I.V.Belyaeva. № 4655. K |
| 66 | S. alba | 0556278 Germany, Hesse nursery, Baumschulen, 7/05/1987. F.G.Meyer. (NA 44016) NA |
| 67 | S. alba | Turkey, B-1, Izmir—Manisa. A.P.Khokhryakov, M.T.Mazurenko/A.K.Skvortsov? MHA |
| 68 | S. alba | Armenia, Vedinsky district, Saray-bulak gorge. A.K.Skvortsov. MHA |
| 69 | S. alba | North Turkey, B8, Erzurum, Palandeken Mountains. A.K.Skvortsov. MHA |
| 70 | S. alba | Iran, Isfahan Province. A.K.Skvortsov. MHA |
| 71 | S. excelsa | Azerbaijan, Kuba district, Cuba-Derbent. A.K.Skvortsov. MHA |
| 72 | S. excelsa | Afghanistan, Takhar Province, about 3 km south of Taloqan. A.K.Skvortsov/I.V.Belyaeva. MHA |
| 73 | S. alba | Western Georgia, Arsian Ridge, road to Goderdza Pass. E.E. Gogina. MHA |
| 74 | S. alba | Azerbaijan, Zuvand basin. A.K.Skvortsov. MHA |
| 75 | S. fragilis | Armenia, Meghri district, okr. Tashtun village. E.E. Gogina, Proskuryakova. MHA |
| 76 | S. alba | Iran, Gilan province, Pahlavi city (now Bandar Anzali). A.K.Skvortsov. MHA |
References
- Skvortsov, A.K. Willows of Russia and Adjacent Countries: Taxonomical and Geographical Revision; University of Joensuu Faculty of Mathematics and Natural Sciences Report Series; University of Joensuu: Joensuu, Finland, 1999; Volume 39. [Google Scholar]
- Argus, G.W. Salix. In Flora of North America north of Mexico; Flora of North America Editorial Committee, Ed.; Oxford University Press: New York, NY, USA, 2010; Volume 7, pp. 23–162. [Google Scholar]
- Gramlich, S.G.; Wagner, N.D.; Horandl, E. RAD-seq reveals genetic structure of the F2-generation of natural willow hybrids (Salix L.) and a great potential for interspecific introgression. BMC Plant Biol. 2018, 18, 317. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- Wagner, N.D.; He, L.; Horandl, E. Phylogenomic relationships and evolution of polyploid Salix species revealed by RAD sequencing data. Front. Plant Sci. 2020, 11, 1077. [Google Scholar] [CrossRef] [PubMed]
- Marchenko, A.M.; Kuzovkina, Y.A. Calculation of the ovule number in the genus Salix: A method for taxa differentiation. Appl. Plant Sci. 2021, 9, e11450. [Google Scholar] [CrossRef] [PubMed]
- Skvortsov, A.K.; Golisheva, M.D. Issledovanie anatomii lista uv v svyazi s sistematikoy roda i semeistva. [A study of the leaf anatomy of Salix for the systematics of the genus and the family]. Acta Bot. 1966, 12, 125–174. (In Russian) [Google Scholar]
- Fang, Z.-F.; Zhao, S.-D.; Skvortsov, A.K. Salicaceae. In Flora of China; Wu, Z.-Y., Raven, P.H., Eds.; Science Press: Beijing China; Missouri Botanical Garden Press: St. Louis, MO, USA, 1999; Volume 4, pp. 162–274. [Google Scholar]
- Santamour, F.S.; McArdle, A.J. Cultivars of Salix babylonica and other weeping willows. J. Arboric. 1988, 14, 180–184. [Google Scholar] [CrossRef]
- Meikle, R.D. Willows and Poplars of Great Britain and Ireland; Botanical Society of the British Isles: London, UK, 1984. [Google Scholar]
- Triest, L.; De Greef, B.; Vermeersch, S.; Van Slycken, J.; Coart, E. Genetic variation and putative hybridisation in Salix alba and Salix fragilis: Evidence from allozyme data. Plant Syst. Evol. 2000, 215, 169–187. [Google Scholar] [CrossRef]
- Triest, L. Hybridization in staminate and pistillate Salix alba and S. fragilis (Salicaceae): Morphology versus RAPDs. Plant Syst. Evol. 2001, 226, 143–154. [Google Scholar] [CrossRef]
- De Cock, K.; Lybeer, B.; Vander Mijnsbrugge, K.; Zwaenepoel, A.; Van Peteghem, P.; Quataert, P.; Breyne, P.; Goetghebeur, P.; Slycken, J.V. Diversity of the willow complex Salix alba–S. x rubens-S-fragilis. Silvae Genet. 2003, 52, 148–153. [Google Scholar]
- King, R.A.; Harris, S.L.; Karp, A. Characterization and inheritance of nuclear microsatellite loci for use in population studies of the allotetraploid Salix alba–Salix fragilis complex. Tree Genet. Genomes 2010, 6, 247–258. [Google Scholar] [CrossRef]
- Skvortsov, A.K. Sovremennoye rasprostraneniye i veroyatnyĭ pervichnyĭ areal lomkoĭ ivy (Salix fragilis L.) [Present distribution and probable primary range of brittle willow (Salix fragilis L.)]. In Problemy Biogeotsenologii, Geobotaniki i Botanicheskoĭ Geografii [Problems in Biogeocoenology, Geobotany and Botanical Geography]; Tikhomirov, B.A., Ed.; Nauka: Leningrad, Russia, 1973; pp. 236–278. Available online: http://www.salicicola.com/translations/Skv1973SF.html (accessed on 20 January 2023)(In Russian, English Translation).
- Marchenko, A.M.; Kuzovkina, Y.A. Notes on the nomenclature and taxonomy of Salix fragilis (Salicaceae). Taxon 2022, 71, 721–732. [Google Scholar] [CrossRef]
- Meneghetti, S.; Barcaccia, G.; Paiero, P.; Lucchin, M. Genetic characterization of Salix alba L. and Salix fragilis L. by means of different PCR-derived marker systems. Plant Biosyst. 2007, 141, 283–291. [Google Scholar] [CrossRef]
- Kehl, A.; Aas, G.; Rambold, G. Genotypical and multiple phenotypical traits discriminate Salix × rubens Schrank clearly from its parent species. Plant Syst. Evol. 2008, 275, 169–179. [Google Scholar] [CrossRef]
- Oberprieler, C.; Dietz, L.; Harlander, C.; Heilmann, J. Molecular and phytochemical evidence for the taxonomic integrity of Salix alba, S. fragilis, and their hybrid S. ×rubens (Salicaceae) in mixed stands in SE Germany. Plant Syst. Evol. 2013, 299, 1107–1118. [Google Scholar] [CrossRef]
- Barcaccia, G.; Meneghetti, S.; Lucchin, M.; De Jong, H. Genetic segregation and genomic hybridization patterns support an allotetraploid structure and disomic inheritance for Salix species. Diversity 2014, 6, 633–651. [Google Scholar] [CrossRef] [Green Version]
- Wu, J.; Nyman, T.; Wang, D.-C.; Argus, G.W.; Yang, Y.-P.; Chen, J.-H. Phylogeny of Salix subgenus Salix s.l. (Salicaceae): Delimitation, biogeography, and reticulate evolution. BMC Evol. Biol. 2015, 15, 31. [Google Scholar] [CrossRef] [Green Version]
- Sitzia, T.; Barcaccia, G.; Lucchin, M. Genetic diversity and stand structure of neighboring white willow (Salix alba L.) populations along fragmented riparian corridors: A case study. Silvae Genet. 2018, 67, 79–88. [Google Scholar] [CrossRef] [Green Version]
- Barcaccia, G.; Meneghetti, S.; Albertini, E.; Triest, L.; Lucchin, M. Linkage mapping in tetraploid willows: Segregation of molecular markers and estimation of linkage phases support an allotetraploid structure for Salix alba × Salix fragilis interspecific hybrids. Heredity 2003, 90, 169–180. [Google Scholar] [CrossRef]
- Primack, R.B. Relationships among flowers, fruits, and seeds. Annu. Rev. Ecol. Syst. 1987, 18, 409–430. [Google Scholar] [CrossRef]
- Endress, P.K. Angiosperm ovules: Diversity, development, evolution. Ann. Bot. 2011, 107, 1465–1489. [Google Scholar] [CrossRef] [Green Version]
- Strelin, M.M.; Aizen, M.A. The interplay between ovule number, pollination and resources as determinants of seed set in a modular plant. PeerJ 2018, 6, e5384. [Google Scholar] [CrossRef]
- Chmelař, J. Taxonomický význam pocˇtu zakladu semen kapslí u rodu Salix L. [Taxonomic importance of capsule seed number in the genus Salix L.]. Acta Mus. Sil. Ser. C Dendrol. 1977, 26, 1–7. (In Czech) [Google Scholar]
- Argus, G.W. The genus Salix (Salicaceae) in the southeastern United States. Syst. Bot. Monogr. 1986, 9, 1–170. [Google Scholar] [CrossRef]
- Valyagina-Malutina, E.T. Willows of the European Part of Russia; KMK: Moscow, Russia, 2004. (In Russian) [Google Scholar]
- Marchenko, A.M. Semyazachatki i Identifikaciya iv (Salix) [Ovules and Identification of Willows (Salix)]; Publishing House: Moscow, Russia, 2019. (In Russian) [Google Scholar]
- Marchenko, A.M.; Kuzovkina, Y.A. Identification of hybrid formulae of a few willows (Salix) using ovule numbers. Silvae Genet. 2021, 70, 75–83. [Google Scholar] [CrossRef]
- INTA. 2021. Available online: https://inta.gob.ar/variedades/soveny-americano (accessed on 30 June 2022).
- Ragonese, A.E.; Alberti, F.R. Sauces hibridas originados naturalmente en la Republica Argentina. Rev. Investig. Agric. 2015, 12, 111–153. (In Spanish) [Google Scholar]
- Krüssmann, G. Manual of Cultivated Broad-Leaved Trees and Shrubs; Timber Press: Beaverton, OR, USA, 1984. [Google Scholar]
- Dirr, M.A. Manual of Woody Landscape Plants: Their Identification, Ornamental Characteristics Culture, Propagation and Uses, 6th ed.; Stipes Publishing: Champaign, IL, USA, 2009. [Google Scholar]
- Vermont Willow Nursery. Salix matsudana. 2021. Available online: https://www.willowsvermont.com/home.html (accessed on 15 July 2021).
- Ohashi, H.; Yonekura, K. Additions and corrections for Salicaceae of Japan 3. J. Jpn. Bot. 2015, 90, 1–14. [Google Scholar]
- Bailey, L.H. Cyclopedia of American Horticulture; Virtue: Toronto, ON, Canada, 1902; Volume 4, p. 1600. [Google Scholar]
- Bailey, L.H. The Standard Cyclopedia of Horticulture; Macmillan, 1917; Volume 6, p. 3053. [Google Scholar]
- Rehder, A. Bibliography of Cultivated Trees and Shrubs; Arnold Arboretum of Harvard University: Jamaica Plain, MA, USA, 1949. [Google Scholar]
- Cronk, Q.; Ruzzier, E.; Belyaeva, I.; Percy, D. Salix transect of Europe: Latitudinal patterns in willow diversity from Greece to arctic Norway. Biodivers. Data J. 2015, 3, e6258. [Google Scholar] [CrossRef] [Green Version]
- Christensen, K.; Jonsell, B. Proposal to conserve the name Salix fragilis with a conserved type (Salicaceae). Taxon 2005, 54, 555–556. [Google Scholar] [CrossRef]
Figure 1.
(Left) Narrow-lanceolate leaves of S. babylonica ’Babylon’ (left) and lanceolate leaves of S. babylonica var. sacramenta (right). (Center) The green-gray bark of S. babylonica var. sacramenta retains its color even on the side exposed to the sun. Right: S. babylonica var. sacramenta in the Paraná Delta region, Argentina (photo by T. Cerrillo).
Figure 1.
(Left) Narrow-lanceolate leaves of S. babylonica ’Babylon’ (left) and lanceolate leaves of S. babylonica var. sacramenta (right). (Center) The green-gray bark of S. babylonica var. sacramenta retains its color even on the side exposed to the sun. Right: S. babylonica var. sacramenta in the Paraná Delta region, Argentina (photo by T. Cerrillo).
Figure 2.
Salix babylonica var. sacramenta. Leaf margin (left). Branchlet with the bud (right).
Figure 3.
Herbarium specimen of S. babylonica ‘Babylon’ (NA0263746) of the live specimen NA44011 (left). The green-brown bark of branches of S. babylonica ‘Babylon’ NA44011 growing at Storrs, Connecticut, US, gets tanned, gaining purple color on the upper side exposed to the sun (center). S. babylonica ‘Babylon’ NA44011 growing at the National Arboretum, Washington, US, displays its strongly pendulous habit (right) (photo by H. Svoboda).
Figure 3.
Herbarium specimen of S. babylonica ‘Babylon’ (NA0263746) of the live specimen NA44011 (left). The green-brown bark of branches of S. babylonica ‘Babylon’ NA44011 growing at Storrs, Connecticut, US, gets tanned, gaining purple color on the upper side exposed to the sun (center). S. babylonica ‘Babylon’ NA44011 growing at the National Arboretum, Washington, US, displays its strongly pendulous habit (right) (photo by H. Svoboda).
Figure 4.
Outermost cataphylls of S. babylonica var. sacramenta (left), S. babylonica ’Babylon’ (center) and S. babylonica L. var. matsudana ‘Umbraculifera’ (right) after the bud scales were removed. In both taxa of S. babylonica—var. sacramenta and ’Babylon’—hairs were located only above the central vein and along the edge so that the part of the cataphyll blade lying between the central vein and the edge, remained glabrous, also there were no hairs on its top. In the cataphylls of S. matsudana ‘Umbraculifera’, the abaxial side is densely and evenly pubescent with long hairs.
Figure 4.
Outermost cataphylls of S. babylonica var. sacramenta (left), S. babylonica ’Babylon’ (center) and S. babylonica L. var. matsudana ‘Umbraculifera’ (right) after the bud scales were removed. In both taxa of S. babylonica—var. sacramenta and ’Babylon’—hairs were located only above the central vein and along the edge so that the part of the cataphyll blade lying between the central vein and the edge, remained glabrous, also there were no hairs on its top. In the cataphylls of S. matsudana ‘Umbraculifera’, the abaxial side is densely and evenly pubescent with long hairs.
Figure 5.
Bud scales and pubescent outermost cataphylls of S. babylonica var. matsudana ‘Umbraculifera’ (left). A unique dense subglobose crown of S. babylonica var. matsudana ‘Umbraculifera’ (center) (photos by M. Dodge). Upright habit of S. babylonica var. matsudana ‘Umbraculifera’ (left) and pendulous habit of S. babylonica ’Babylon’ (right) visible during their first year of growth (right).
Figure 5.
Bud scales and pubescent outermost cataphylls of S. babylonica var. matsudana ‘Umbraculifera’ (left). A unique dense subglobose crown of S. babylonica var. matsudana ‘Umbraculifera’ (center) (photos by M. Dodge). Upright habit of S. babylonica var. matsudana ‘Umbraculifera’ (left) and pendulous habit of S. babylonica ’Babylon’ (right) visible during their first year of growth (right).
Figure 6.
Stipules of S. babylonica var. matsudana ‘Umbraculifera’ (left, center) and S. babylonica ’Babylon’ (right).
Figure 6.
Stipules of S. babylonica var. matsudana ‘Umbraculifera’ (left, center) and S. babylonica ’Babylon’ (right).
Figure 7.
Diagrammatic representation of the variation of the ovule number in S. babylonica—S. fragilis—S. alba complex: the pure species and intermediate variants.
Figure 7.
Diagrammatic representation of the variation of the ovule number in S. babylonica—S. fragilis—S. alba complex: the pure species and intermediate variants.
Table 1.
The ovule data for S. babylonica. Each capsule in Salix has 2 valves and the presented data include the percentage of valves in a catkin with different numbers of ovules. Additional characteristics are included: the number of ovules per ovary (min/often and max/often), the ovule indices (the minimum and maximum number of ovules per ovary), presence of trichomes at bract apex (A—bracts abscised; N—none; L—long; S—short), number of nectaries, ovary pubescence (G—glabrous; P—pubescent) and number of studied ovaries.
Table 1.
The ovule data for S. babylonica. Each capsule in Salix has 2 valves and the presented data include the percentage of valves in a catkin with different numbers of ovules. Additional characteristics are included: the number of ovules per ovary (min/often and max/often), the ovule indices (the minimum and maximum number of ovules per ovary), presence of trichomes at bract apex (A—bracts abscised; N—none; L—long; S—short), number of nectaries, ovary pubescence (G—glabrous; P—pubescent) and number of studied ovaries.
| No | Specimen | Percentage of Valves with Each Ovule Number | No. of Ovules per Ovary | Ovule Index | Trichomes | Nectaries | Ovary | No of Ovaries | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | Min/ Often | Max/ Often | |||||||
| 1 | S. babylonica var. sacramenta ‘Soveny Americano’ | 61 | 39 | 2/2 | 3/3 | 2–3 | A | 1 | G | 50 | ||
| 2 | S. babylonica | 28 | 72 | 2/3 | 4/4 | 2–4 | A | 1 | G | 68 | ||
| 3 | Salix—specimen No. 1 in the folder “S. babylonica” | 17 | 83 | 2/3 | 4/4 | 2–4 | A | 1 | G | 58 | ||
| 4 | Salix—specimen No. 2 in the folder “S. babylonica.” | 16 | 84 | 2/3 | 4/4 | 2–4 | A | 2 | G | 50 | ||
| 5 | Salix—specimen No. 3 in the folder “S. babylonica” | 9 | 91 | 2/3 | 4/4 | 2–4 | A | 2 | G | 92 | ||
| 6 | S. babylonica | 8 | 92 | 2/3 | 4/4 | 2–4 | A | 1 | G | 56 | ||
| 7 | S. babylonica | 5 | 95 | 3/4 | 4/4 | 3–4 | A | 2 | G, P | 130 | ||
| 8 | S. babylonica | 4 | 96 | 3/4 | 4/4 | 3–4 | A | 1 | G | 60 | ||
| 9 | S. babylonica | 1 | 99 | 3/4 | 4/4 | 3–4 | A | 1 | P | 58 | ||
| 10 | S. babylonica ‘Babylon’ | 1 | 99 | 3/4 | 4/4 | 3–4 | A | 1 | G | 119 | ||
| 11 | S. babylonica var. annularis | 8 | 92 | 3/3 | 4/4 | 3–4 | A | 1 | P at base | 109 | ||
| 12 | S. matsudana f. tortuosa | 4 | 96 | 3/3 | 4/4 | 3–4 | A | 1 | G | 56 | ||
| 13 | S. babylonica ‘Tortuosa’ | 1 | 99 | 3/4 | 4/4 | 3–4 | A | 1 | G | 46 | ||
| 14 | S. matsudana ‘Tortuosa’ | 0 | 100 | 4/4 | 4/4 | 4–4 | A | 1 | G | 52 | ||
| 15 | S. matsudana var. tortuosa | 0 | 100 | 4/4 | 4/4 | 4–4 | A | 1 | G | 55 | ||
| 16 | S. matsudana | 0 | 100 | 4/4 | 4/4 | 4–4 | A | 1 | G | 32 | ||
| 17 | S. matsudana | 0 | 100 | 4/4 | 4/4 | 4–4 | A | 1 | G | 65 | ||
| 18 | S. matsudanaf. pendula | 0 | 100 | 4/4 | 4/4 | 4–4 | A | 1 | P | 56 | ||
| 19 | S. babylonica | 3 | 96 | 1 | 3/4 | 5/4 | 3–5 | A | 1, 2 | G, P | 91 | |
| 20 | S. matsudana | 1 | 98 | 1 | 3/4 | 5/4 | 3–5 | A | 1 | G | 105 | |
| 21 | S. matsudana var. tortuosa | 1 | 93 | 6 | 3/4 | 5/5 | 3–5 | A | 1 | G | 97 | |
| 22 | S. babylonica ‘Tortuosa | 0 | 99 | 1 | 4/4 | 5/4 | 4–5 | A | 1 | G | 56 | |
| 23 | S. matsudana ‘Umbraculifera’ | 0 | 85 | 15 | 4/4 | 6/5 | 4–6 | A | 1, 2 | G | 35 | |
| 24 | S. matsudana ‘Umbraculifera’ | 0 | 78 | 22 | 4/4 | 6/5 | 4–6 | A | 1 | G | 45 | |
| 25 | S. babylonica | 0 | 80 | 20 | 4/4 | 6/5 | 4–6 | A | 1 | G | 20 | |
| 26 | S. babylonica | 0 | 99 | 1 | 4/4 | 5/4 | 4–5 | A | 1, 2 | G, P | 132 | |
| 27 | S. babylonica | 0 | 98 | 2 | 4/4 | 5/4 | 4–5 | A | 1 | G | 191 | |
| 28 | S. babylonica | 0 | 97 | 3 | 4/4 | 5/4 | 4–5 | A | 1 | G | 57 | |
| 29 | S. fragilis | 10 | 61 | 29 | 2/4 | 6/5 | 2–6 | L | 1 | G | 38 | |
| 30 | S. fragilis | 3 | 24 | 56 | 17 | 2/4 | 8/6 | 2–8 | L | 1 | G | 38 |
Table 2.
The ovule data for Salix alba, S. fragilis and S. alba × S. fragilis with 1 to 6 ovule/valve. Each capsule in Salix has 2 valves and the presented data include the percentage of valves in a catkin with different numbers of ovules. The additional characteristics are included: the number of ovules per ovary (min/often and max/often), the ovule indices (the minimum and maximum number of ovules per ovary), presence of trichomes at bract apex (A—bracts abscised; L—long; N—none; S—short), and number of studied ovaries. The entries with the specimens’ numbers (column 1) were colored according to their names based on their original identification—blue for S. alba, yellow for S. fragilis, red for S. alba × S. fragilis—for visual presentation of the species’ distribution throughout the tables.
Table 2.
The ovule data for Salix alba, S. fragilis and S. alba × S. fragilis with 1 to 6 ovule/valve. Each capsule in Salix has 2 valves and the presented data include the percentage of valves in a catkin with different numbers of ovules. The additional characteristics are included: the number of ovules per ovary (min/often and max/often), the ovule indices (the minimum and maximum number of ovules per ovary), presence of trichomes at bract apex (A—bracts abscised; L—long; N—none; S—short), and number of studied ovaries. The entries with the specimens’ numbers (column 1) were colored according to their names based on their original identification—blue for S. alba, yellow for S. fragilis, red for S. alba × S. fragilis—for visual presentation of the species’ distribution throughout the tables.
| No | Specimen | Percentage of Valves with Each Ovule Number | No. of Ovules per Ovary | Ovule Index | Trichomes | No of Ovaries | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2 | 3 | 4 | 5 | 6 | Min/ Often | Max/ Often | |||||
| 1 | S. fragilis f. latifolia | 33 | 67 | 0 | 0 | 0 | 4/4 | 6/6 | 4–6 | L | 70 |
| 2 | S. alba | 27 | 73 | 0 | 0 | 0 | 4/5 | 6/6 | 4–6 | L | 44 |
| 3 | S. alba × S. fragilis | 12 | 88 | 0 | 0 | 0 | 5/5 | 6/6 | 5–6 | L | 82 |
| 4 | S. alba | 2 | 98 | 0 | 0 | 0 | 5/6 | 6/6 | 5–6 | N | 18 |
| 5 | S. aegyptiaca | 1 | 99 | 0 | 0 | 0 | 5/6 | 6/6 | 5/6 | L | 72 |
| 6 | S. euxina | 0 | 100 | 0 | 0 | 0 | 6/6 | 6/6 | 6/6 | L | 45 |
| 7 | S. alba | 3 | 94 | 3 | 0 | 0 | 4/6 | 7/7 | 4–7 | S | 75 |
| 8 | S. fragilis | 3 | 80 | 17 | 0 | 0 | 5/6 | 8/7 | 5–8 | N | 75 |
| 9 | S. fragilis | 1 | 76 | 23 | 0 | 0 | 6/6 | 8/7 | 6–8 | L | 51 |
| 10 | S. fragilis | 1 | 53 | 44 | 2 | 0 | 6/6 | 9/8 | 6–9 | L | 48 |
| 11 | S. fragilis var. decipiens | 3 | 50 | 33 | 14 | 0 | 4/6 | 9/8 | 4–9 | N | 30 |
| 12 | S. alba | 1 | 50 | 47 | 2 | 0 | 6/6 | 9/7 | 6–9 | S | 146 |
| 13 | S. alba | 0 | 98 | 2 | 0 | 0 | 6/6 | 7/6 | 6–7 | S | 70 |
| 14 | S. fragilis | 0 | 93 | 7 | 0 | 0 | 6/6 | 7/6 | 6–7 | L | 65 |
| 15 | S. alba | 0 | 92 | 8 | 0 | 0 | 6/6 | 7/6 | 6–7 | A | 18 |
| 16 | S. alba | 0 | 90 | 10 | 0 | 0 | 6/6 | 7/6 | 6–7 | A | 35 |
| 17 | S. fragilis | 0 | 90 | 10 | 0 | 0 | 6/6 | 7/6 | 6–7 | L | 92 |
| 18 | S. fragilis | 0 | 89 | 11 | 0 | 0 | 6/6 | 8/7 | 6–8 | A | 66 |
| 19 | S. alba | 0 | 89 | 11 | 0 | 0 | 6/6 | 8/7 | 6–8 | S | 106 |
| 20 | S. fragilis × S. alba | 0 | 64 | 36 | 0 | 0 | 6/6 | 8/7 | 6–8 | S | 40 |
| 21 | S. fragilis (×S. alba?) | 0 | 56 | 44 | 0 | 0 | 6/6 | 8/7 | 6–8 | L | 39 |
| 22 | S. alba | 0 | 50 | 50 | 0 | 0 | 6/6 | 8/8 | 6–8 | N | 20 |
| 23 | S. alba | 0 | 95 | 3 | 2 | 0 | 6/6 | 8/6 | 6–8 | S | 60 |
| 24 | S. alba | 0 | 92 | 6 | 2 | 0 | 6/6 | 8/6 | 6–8 | S | 85 |
| 25 | S. alba | 0 | 90 | 7 | 3 | 0 | 6/6 | 9/7 | 6–9 | S | 73 |
| 26 | S. alba | 0 | 79 | 18 | 3 | 0 | 6/6 | 8/7 | 6–8 | A | 14 |
| 27 | S. fragilis × S. alba | 0 | 76 | 23 | 1 | 0 | 6/6 | 8/7 | 6–8 | S | 40 |
| 28 | S. alba | 0 | 74 | 19 | 7 | 0 | 6/6 | 9/7 | 6–9 | S | 31 |
| 29 | S. fragilis | 0 | 70 | 26 | 4 | 0 | 6/6 | 8/8 | 6–8 | S | 73 |
| 30 | S. fragilis | 0 | 56 | 42 | 2 | 0 | 6/6 | 8/7 | 6–8 | L | 44 |
| 31 | S. alba | 0 | 56 | 39 | 5 | 0 | 6/6 | 9/7 | 6–9 | N | 97 |
| 32 | S. alba | 0 | 60 | 35 | 5 | 0 | 6/6 | 9/7 | 6–9 | S | 71 |
| 33 | S. fragilis | 0 | 38 | 52 | 10 | 0 | 6/7 | 10/8 | 6–10 | L | 54 |
| 34 | S. alba var. caerulea | 0 | 36 | 27 | 37 | 0 | 6/6 | 10/9 | 6–10 | A | 28 |
| 35 | S. fragilis | 0 | 34 | 41 | 25 | 0 | 6/6 | 10/9 | 6–10 | N | 71 |
| 36 | S. alba | 0 | 27 | 46 | 27 | 0 | 6/6 | 10/9 | 6–10 | N | 33 |
| 37 | S. alba | 0 | 25 | 59 | 16 | 0 | 6/7 | 10/9 | 6–10 | N | 65 |
| 38 | S. alba | 0 | 24 | 33 | 43 | 0 | 6/7 | 10/8 | 6–10 | N | 63 |
| 39 | S. fragilis | 0 | 23 | 67 | 10 | 0 | 6/7 | 10/9 | 6–10 | N | 73 |
| 40 | S. fragilis | 0 | 19 | 63 | 18 | 0 | 6/7 | 10/9 | 6–10 | N | 63 |
| 41 | S. fragilis | 0 | 15 | 62 | 23 | 0 | 6/8 | 10/9 | 6–10 | L | 41 |
| 42 | S. fragilis × S. alba | 0 | 13 | 84 | 3 | 0 | 6/7 | 10/8 | 6–10 | A | 91 |
| 43 | S. fragilis | 0 | 13 | 81 | 6 | 0 | 7/8 | 9/8 | 7–9 | L | 34 |
| 44 | S. alba × S. fragilis | 0 | 10 | 53 | 27 | 0 | 6/8 | 10/9 | 6–10 | N | 31 |
| 45 | S. fragilis | 0 | 4 | 65 | 31 | 0 | 7/8 | 10/9 | 7–10 | S | 70 |
| 46 | S. alba | 0 | 4 | 30 | 66 | 0 | 8/9 | 10/9 | 8–10 | S | 69 |
| 47 | S. fragilis | 0 | 3 | 41 | 56 | 0 | 8/9 | 10/9 | 8–10 | A | 43 |
| 48 | S. fragilis | 0 | 3 | 56 | 39 | 2 | 7/8 | 11/10 | 7–11 | L | 94 |
| 49 | S. euxina | 0 | 26 | 46 | 26 | 2 | 7/8 | ? | 7–10 | L | 51 |
| 50 | S. fragilis | 0 | 19 | 54 | 23 | 4 | 7/8 | 10/9 | 7–10 | L | 39 |
| 51 | Salix | 0 | 0 | 30 | 70 | 0 | 8/9 | 10 | 8–10 | S | 15 |
| 52 | S. alba | 0 | 0 | 21 | 79 | 0 | 9 | 10 | 9–10 | N | 14 |
| 53 | Salix | 0 | 0 | 4 | 96 | 0 | 9 | 10 | 9–10 | S | 12 |
| 54 | Salix | 0 | 0 | 3 | 97 | 0 | 9 | 10 | 9–10 | N | 16 |
| 55 | S. alba | 0 | 0 | 25 | 74 | 1 | 8/9 | 11/10 | 8–11 | S | 55 |
| 56 | S. fragilis | 0 | 0 | 44 | 51 | 5 | 8/9 | 12/10 | 8–12 | S | 38 |
| 57 | S. alba | 0 | 0 | 14 | 79 | 7 | 9/9 | 11/10 | 9–11 | N | 22 |
| 58 | S. alba × S. fragilis | 0 | 0 | 10 | 88 | 2 | 8/9 | 11/10 | 8–11 | S | 26 |
| 59 | S. alba | 0 | 0 | 4 | 95 | 1 | 9/9 | 11/10 | 9–11 | N | 65 |
| 60 | S. alba | 0 | 0 | 2 | 84 | 14 | 9/10 | 12 | 9–12 | A | 58 |
| 61 | S. alba | 0 | 0 | 1 | 78 | 21 | 10/10 | 12/11 | 10–12 | N | 36 |
| 62 | S. alba | 0 | 0 | 4 | 46 | 50 | 10 | 12/11 | 10–12 | N | 12 |
| 63 | S. alba var. splendens | 0 | 0 | 0 | 93 | 7 | 10 | 12/11 | 10–12 | N | 14 |
| 64 | S. alba | 0 | 0 | 0 | 80 | 20 | 10 | 12 | 10–12 | A | 20 |
| 65 | S. alba | 0 | 0 | 0 | 71 | 29 | 10 | 12 | 10–12 | N | 12 |
| 66 | S. alba | 0 | 0 | 0 | 63 | 37 | 10 | 12 | 10–12 | N | 38 |
Table 3.
The ovule data for Salix alba, S. fragilis and S excelsa with 6 to 12 ovule/valve. Each capsule in Salix has 2 valves and the presented data include the percentage of valves in a catkin with different numbers of ovules. The additional characteristics are included: the number of ovules per ovary (min/often and max/often), the ovule indices (the minimum and maximum number of ovules per ovary), presence of trichomes at bract apex (A—bracts abscised; N—none; S—short), and number of studied ovaries. The entries with the specimens’ numbers (column 1) were colored according to their names based on their original identification—blue for S. alba, yellow for S. fragilis, white for S. excelsa—for visual presentation of the species’ distribution throughout the tables.
Table 3.
The ovule data for Salix alba, S. fragilis and S excelsa with 6 to 12 ovule/valve. Each capsule in Salix has 2 valves and the presented data include the percentage of valves in a catkin with different numbers of ovules. The additional characteristics are included: the number of ovules per ovary (min/often and max/often), the ovule indices (the minimum and maximum number of ovules per ovary), presence of trichomes at bract apex (A—bracts abscised; N—none; S—short), and number of studied ovaries. The entries with the specimens’ numbers (column 1) were colored according to their names based on their original identification—blue for S. alba, yellow for S. fragilis, white for S. excelsa—for visual presentation of the species’ distribution throughout the tables.
| No | Specimen | Percentage of Valves with Each Ovule Number | No. of Ovules per Ovary | Ovule Index | Trichomes | No of Ovaries | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 6 | 7 | 8 | 9 | 10 | 11 | 12 | Min/ Often | Max/ Often | |||||
| 67 | S. alba | 91 | 7 | 2 | 0 | 0 | 0 | 0 | 11/12 | 14 | 11–14 | N | 42 |
| 68 | S. alba | 2 | 5 | 78 | 15 | 0 | 0 | 0 | 13/16 | 17 | 13–17 | A | 48 |
| 69 | S. alba | 0 | 5 | 84 | 11 | 0 | 0 | 0 | 14/16 | 18 | 14–18 | S | 55 |
| 70 | S. alba | 0 | 24 | 71 | 5 | 0 | 0 | 0 | 15 | 17 | 15–17 | N | 19 |
| 71 | S. excelsa | 0 | 5 | 67 | 28 | 0 | 0 | 0 | 15 | 18 | 15–18 | N | 9 |
| 72 | S. excelsa | 0 | 0 | 14 | 73 | 9 | 3 | 1 | 16/17 | 21/18 | 16–21 | N | 54 |
| 73 | S. alba | 0 | 0 | 0 | 88 | 8 | 4 | 0 | 18 | 20 | 18–20 | N | 36 |
| 74 | S. alba | 0 | 0 | 0 | 62 | 20 | 9 | 9 | 18 | 21/19 | 18–21 | A | 17 |
| 75 | S. fragilis | 0 | 0 | 0 | 55 | 27 | 9 | 9 | 18/19 | 22/19 | 18–22 | A | 11 |
| 76 | S. alba | 0 | 0 | 0 | 0 | 26 | 48 | 26 | 20/21 | 24/23 | 20–24 | A | 27 |
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Share and Cite
MDPI and ACS Style
Marchenko, A.M.; Kuzovkina, Y.A. The Ovule Number Variation Provides New Insights into Taxa Delimitation in Willows (Salix subgen. Salix; Salicaceae). Plants 2023, 12, 497. https://doi.org/10.3390/plants12030497
AMA Style
Marchenko AM, Kuzovkina YA. The Ovule Number Variation Provides New Insights into Taxa Delimitation in Willows (Salix subgen. Salix; Salicaceae). Plants. 2023; 12(3):497. https://doi.org/10.3390/plants12030497
Chicago/Turabian StyleMarchenko, Alexander M., and Yulia A. Kuzovkina. 2023. "The Ovule Number Variation Provides New Insights into Taxa Delimitation in Willows (Salix subgen. Salix; Salicaceae)" Plants 12, no. 3: 497. https://doi.org/10.3390/plants12030497
Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.
