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Article

Morphological and Anatomical Characterization of Stems in Lilium Taxa

by
Peng Zhou
1,†,
Kuangkuang Liao
1,†,
Xiunian Feng
1,
Rui Liang
2,
Nianjun Teng
2 and
Fang Du
1,*
1
College of Urban and Rural Construction, Shanxi Agricultural University, Jinzhong 030801, China
2
College of Horticulture, Nanjing Agricultural University, Nanjing 210095, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Horticulturae 2025, 11(5), 546; https://doi.org/10.3390/horticulturae11050546
Submission received: 2 April 2025 / Revised: 13 May 2025 / Accepted: 15 May 2025 / Published: 18 May 2025
(This article belongs to the Section Floriculture, Nursery and Landscape, and Turf)
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Abstract

:
Lilium holds significant horticultural and ecological importance. Understanding the morpho-anatomical diversity of the stems can provide insights into taxonomy and breeding strategies. This study comprehensively examined the stem morpho-anatomy of 71 Lilium taxa to elucidate taxonomic and structural differences. For the first time, four distinct jigsaw-puzzle-shaped shapes of epidermal cells (Ep) in monocot stems, novel I-shaped and Co-xylem (O-, X-, W-, Q-shaped) vascular bundles (Vb) in Lilium stems, and quantitative characteristics (Vb density, xylem/phloem area ratio, etc.) were systematically discovered and analyzed. Asiatic (A) and Longiflorum × A (LA) hybrids displayed epidermal appendages, while Oritenal × Trumpet (OT) hybrids featured thicker sclerenchymatous rings (Sr). Collateral Vb in hybrids visually displayed bicollateral with degraded bundle sheaths (Bs), contrasting with intact circular Bs in wild species. Ward.D clustering categorized Lilium taxa into group A (Oritenal and OT hybrids) and B (A, LA, Trumpet, Longiflorum × Oriental hybrids and wild species), with Mantel’s test identified height, Ep shape, Ep length/width ratio, cortex/Sr thickness ratio and Bs integrity as key discriminators. Bending stems exhibited a higher Vb area. These findings establish a comprehensive pheno-anatomical framework for Lilium, which can guide future breeding programs and ecological studies.

1. Introduction

The genus Lilium (Liliaceae), renowned for its rich diversity of wild species and hybrid cultivars, holds significant ecological and horticultural importance. Comprising 100–115 species, this genus is predominantly distributed across cold and temperate regions of the Northern Hemisphere, with 55 species native to China [1]. Taxonomic classifications of Lilium have relied on morphological characteristics, among which Comber’s system, dividing the genus into seven sections, remains widely accepted [2]. To date, over 10,000 cultivars has been developed through interspecific and inter-sectional hybridization, categorized into several groups including Asiatic (A), Oriental (O), Longiflorum (L), Trumpet (T), O × T (OT) hybrids and A/L × A (LA) hybrids [3]. Molecular and cytological evidence has corroborated the classification framework [4,5]. Despite advancements in the floral morphology and molecular phylogenetics, the structural intricacies of Lilium stems remain under-explored.
Stems, beyond their functional roles in bio-mechanical support and resource allocation, exhibit phenotypic plasticity in color, texture and morphology traits. These traits enhance landscape esthetics, framing stems as evolutionary adaptations and focal points for ornamental plants breeding [6]. Understanding the morphological diversity of Lilium stems is essential for elucidating adaptive evolution, taxonomic classification and potential innovations in ornamental plants.
The absence of systematic studies on the anatomical structures of Lilium stems has limited insights into domestication-driven adaptive evolution and has impeded the breeding of structurally resilient cultivars. The architecture of plant stems also reflects an evolutionary balance between developmental constraints and environmental pressures. Integrating macro-scale features (e.g., geometry) with micro-scale traits (e.g., tissue patterns) reveals their combined role in the bio-mechanical performance and stress resilience. For instance, the cuticle state (e.g., sinuate vs. smooth) and epidermal appendages (e.g., trichomes, papillae) critically regulate drought adaptation [7,8]. In Cyperaceae, bract-derived mechanical constraints drive diversification in the cross-sectional stem shape (from circular to trigonous to broadly elliptical) [9]. In Lilium, although certain anatomical features (such as the epidermal cell shape, trichome distribution and atactostele organization) have been documented in previous studies, systematic comparative analyses of stem architectures among hybrid lineages (e.g., OT, LA) and wild species are still lacking [10]. Moreover, the diagnostic value of these stem traits in taxonomy and their potential as indicators for breeding stress-resilient cultivars remain largely unresolved.
This study bridges critical knowledge gaps by analyzing 71 Lilium taxa through integrated macro-morphometric and micro-anatomical analyses. We specifically explored whether Lilium among different groups exhibit distinct stem structures, evaluated the taxonomic significance and genetic relationship of stem traits, and investigated how adaptive features correlate with biological resilience. Through the systematic characterization of stems in Lilium, we will develop a pheno-anatomical framework to advance phylogenetic studies and inform the breeding of stress-adapted cultivars.

2. Materials and Methods

2.1. Plant Materials

A panel of 71 Lilium taxa was gathered from an open field at the Baicheng Horticultural Professional Cooperative in Taigu, Shanxi, China (112.29° E, 37.21° N; temperate continental climate) and Baguazhou lily experimental base, Nanjing Agricultural University in Qixia, Nanjing, China (118.83° E, 32.22° N; subtropical monsoon climate). All plant materials were routinely maintained post-planting. To ensure statistical robustness, two independent biological replicates were obtained for each taxon which comprised spatially separated individuals with flower developmental stages. The replicates were subjected to parallel processing throughout subsequent analyses. A detailed overview of plant material is provided in Table 1.

2.2. Phenotyping

At the anthesis of the first flower, descriptive traits (stem coloration, streaking patterns and stem bending) and morphometric traits (plant height and stem diameter) were recorded. Stem curvature was evaluated in accordance with DB11T 1049-2020; Grade of flower products—Cut lily. Beijing Municipal Administration for Market Regulation: Beijing, China, 2021. where it was defined as the downward angle of a horizontally held flower stem. Curvature exceeding 15° was classified as indicative of significant stem bending. Plant height was measured from the soil surface to the plant’s apical meristem, with an accuracy of ± 0.01 cm. Stem diameters were recorded at the midpoint of the stem length with a digital caliper (precision ± 0.01 mm).

2.3. Comparative Cultivation

To assess geotropic responses, bulbs of ‘Mister Sandman’ and ‘Friso’ were planted in two orientations: vertically (in 2023, n = 5 biological replicates) and horizontally (in 2024, n = 5 biological replicates). Both groups were routinely maintained post-planting and entire plants with bulbs were excavated and photographed each autumn.

2.4. Transverse Section Preparation

Three stem specimens were excised at anthesis with 3 cm long at upper region as biological replicates. Firstly they were fixed in 70% ethanol (Tianjin Damao Chemical Reagent Co., Ltd., Tianjin, China, 24 h, room temperature), and processed for freehand sectioning. Sections were sequentially stained with 1% Safranin O (Coolaber, Beijing, China, 24 h), rinsed in 85% ethanol (3 min), counterstained with 0.1% Fast Green FCF (Coolaber, Beijing, China, 5 s), dehydrated through an ethanol–xylene (Tianjin Fuyu Fine Chemical Co., Ltd, Tianjin, China) series (95% ethanol, 3 min; ethanol:xylene = 1:1, 5 min; pure xylene, 5 min), and mounted in neutral balsam (Coolaber, Beijing, China). Imaging was performed using light microscope (Olympus CX33, Olympus, Nagano Prefecture, Japan) and stereomicroscope (Olympus SZX16, Olympus, Nagano Prefecture, Japan) coupled with MShot Image Analysis System (V1.1.4_MSH12, Guangzhou Mingmei Optoelectronic Technology Co., Ltd., Guangzhou, China) and DP Controller 75 (Ver.21, Olympus, Nagano Prefecture, Japan). Workflow details are schematized in Figure 1.

2.5. Descriptive and Quantitative Anatomy of Stems

Stem anatomical traits were analyzed through comparative assessment of both descriptive and quantitative features. Descriptive traits included stem cross-sectional shape, cuticle state, epidermal cells (Ep) shapes, epidermal appendages, cortical projection, vascular bundle (Vb) shape, integrity of bundle sheath (Bs) and pith nature. Ep shape classification was established using a geometric morphometric framework, integrating angular topology and length/width ratio (L/W ratio) thresholds (with ± 0.05 measurement tolerance). Distinct categories were defined: jigsaw-puzzle (polygonal cells with ≥5 vertices); squarish (L/W ratio between 0.95 and 1.10 (inclusive)); radically elongated (L/W ratio < 0.95); and rectangular (L/W ratio > 1.10).
The following quantitative traits were assessed: stem cross-section area (S, mm2), cuticle thickness (μm), Ep L/W ratio (μm/μm), cortex/sclerenchyma thickness (Cx/Sr ratio, μm/μm), Vb density (calculated as the total number of Vbs divided by stem cross-sectional area, No./mm2), Vb component (xylem (Xy), phloem (Ph), vessels (Ve) and xylem parenchyma (Xp)) areas (μm2). These stem cross-sections were radially divided into 16 equal sectors and four opposing 1/16 regions—totaling 25% of the S—were selected [11]. These parameters were measured using ImageJ software (V1.53t, National Institutes of Health, Bethesda, MD, USA).

2.6. Statistical Analysis

Descriptive statistics (mean, range, standard deviation and coefficient of variation (CV)) were computed for morphological and anatomical traits using Microsoft Excel 2021 (Microsoft Corp.) and Origin 2022 (OriginLab Corp.) software. The outliers were defined as data points lying outside 1.5 × interquartile range (IQR) from the quartiles. Three types of multivariate analyses were performed: one-way analysis of variance (ANOVA, IBM SPSS Statistics 27.0), correlation analysis (https://www.omicstudio.cn/), and cluster analysis (https://www.omicstudio.cn/). Data were analyzed using one-way ANOVA to compare height, diameter, cuticle thickness, Cx thickness, Sr thickness and Vb density among lily groups, followed by Duncan’s Multiple Range test for pairwise comparisons. For correlation analysis, Pearson and Mantel’s test methods were used to calculate the correlation coefficients among various morphological and anatomical indices, as well as between these indices and stem bending and lily groups. For cluster analysis, a pairwise matrix of resemblance values was calculated from raw standardized data matrix, using Pearson’s coefficient of resemblance, which is designed for mixed datasets. A dendrogram was generated using the ward.D method.

3. Results

3.1. Morphological Characterization of Lily Stems

Phenotypic diversity was observed among the 71 lily taxa. The stems’ coloration was predominantly green, with 11.27% exhibiting purple hues. Stems of O, T, OT and LO hybrids were smooth, whereas A and LA hybrids displayed distinct streaks. Most accessions displayed straight stems, except for ‘Mister Sandman’ and ‘Beverly Dreams’.
The plant height ranged from 24.60 cm (‘Golden matrix’) to 158.20 cm (‘Orange Planet’), averaging 87.80 cm (CV = 33.12%). T hybrids were significantly taller compared to A hybrids. No significant difference was observed in O, LA, OT and LO hybrids and wild species (p < 0.01, Figure 2A). The stem diameter ranged from 3.79 mm (‘Peach Dwarf’) to 11.45 mm (‘Abbeville’s Pride’), averaging 6.73 mm (CV = 24.07%). LA hybrids had a significantly larger stem diameter compared to wild species (p < 0.01, Figure 2B).

3.2. Growth Posture Analysis

For vertical planting, ‘Friso’ stems grew perpendicular to the soil, while ‘Mister Sandman’ stems initially emerged at a 40° angle and later inclined to 60° (Figure 2C,D). Under horizontal planting, ‘Friso’ stems bent twice to achieve vertical growth, whereas ‘Mister Sandman’ stems curved upward underground and maintained a 60° angle after emergence (Figure 2C,D). Additionally, ‘Mister Sandman’ developed more stem roots than ‘Friso’ (Figure 2C).

3.3. Stem Cross-Section Morphology

Most stem cross-sections examined exhibited a circular or sub-circular configuration (97.18%, Figure 3A), while only ‘Orange Cocotte’ and ‘Sweet Sugar’ displayed irregular patterns (Figure 3C). As a monocot, Lilium stems featured an atactostele arrangement, comprising five distinct layers: Ep, Cx, Sr, vascular cylinder (Vc) and pith (Figure 3A). The single-layered Ep consisted of compact cells lacking intercellular spaces and featured a thick outer cuticle. Beneath the Ep lay the Cx, followed by the Sr. The Vc contains Vbs scattered within loosely arranged parenchymatous cells (Pc), with larger Vbs concentrated centrally (Figure 3B). The pith, devoid of Vbs, was composed of hexagonal Pc. (Figure 3). Lysigenous cavities were observed in four hybrids (‘Armandale’, ‘Paciano’, ‘Purple diamond’ and ‘Unidentified cultivar 3′) (Figure 3D).

3.4. Cuticle Characteristics

The cuticle, located on the Ep’s outer surface, exhibited two primary textures: sinuate (64.79%) and smooth (35.21%) (Figure 4A,B). Smooth cuticles were predominant in LO, O and most OT hybrids, while sinuate cuticles were common in wild species, T hybrids and most A and LA hybrids (Figure 4C). The cuticle thickness ranged from 1.45 µm (‘Navona’) to 4.16 µm (‘Secret kiss’), averaging 2.65 µm (CV = 18.49%) (Figure 4D). No significant differences in the cuticle thickness were observed among Lilium groups (p > 0.01).

3.5. Epidermal Cells Morphology

Epidermal cells displayed diverse shapes, including radically elongated (61.97%, Figure 4A), rectangular (9.86%, Figure 4B), squarish (7.04%, Figure 5A) and jigsaw-puzzle forms (21.13%), resembling ducks, dumbbells, crosses, or horizontal V shapes (Figure 5B,C). Jigsaw-puzzle cells were prevalent in A, T and LA hybrids. Rectangular and squarish cells were rare, primarily observed in O and OT hybrids (Figure 5D).

3.6. Trichomes, Papillae and Stoma

The epidermal appendages, such as trichomes and papillae, were non-ubiquitous in accessions. Glandular trichomes were absent; instead, unicellular hairs (with or without basal cells) were common, while multicellular trichomes were rare (observed only in L. lancifolium) (Figure 6A–D). Papillae arose from Ep protrusions or divisions (Figure 6E–G). Infrequent xerophytic sunken stomata were interspersed among epidermal cells across all accessions (Figure 6H). Trichomes and papillae occurred in 28.17% and 32.39% of accessions, respectively, with minimal overlap (9.86% with trichomes only, 14.08% with papillae only) (Figure 7). These appendages were absent in O, OT and LO hybrids, but present in most A, LA and wild species (Figure 7B,C).

3.7. Cortex and Sclerenchymatous Ring

Transverse stem sections revealed variability in the cortical cell shape and layer number among accessions. The Cx was composed of orbicular or oval Pc, which either tightly packed or had intercellular spaces (Figure 8A,B). Spiny cortical projections were observed in 54.93% of accessions, primarily in A, LA hybrids and wild species, but they were absent in O, OT and LO hybrids (Figure 8C,D). Cortical layers ranged from 2–4 (‘Tarrango’) to 6–9 (‘Sweet Zanica’), with the thickness varying from 75.05 µm (L. pumilum) to 276.87 µm (‘Easy Waltz’), averaging 173.03 µm (CV = 21.78%). O and OT hybrids exhibited a cortical thickness below the mean (Figure 9A).
The Sr consisted of polygonal sclerenchyma cells that were stained red with Safranin O. The Sr layer number and thickness varied among the taxa. Sr layers ranged from 2–3 (‘Sweet Valley’) to 6–11 (‘Mister Sandman’), with the thickness ranging from 78.56 µm (‘Navona’) to 275.66 µm (‘Mister Sandman’), averaging 152.23 µm (CV = 27.19%). OT hybrids significantly displayed thicker Sr compared to other groups (p < 0.01, Figure 9B). The Cx/Sr ratio from 0.95 to 1.05 (inclusive) indicated a comparable thickness, <0.95 denoted thicker Sr and > 1.05 indicated a thicker Cx. Most taxa (84.51%) exhibited a thicker or comparable cortex, while 15.49% had thicker Sr (Figure 9C). OT hybrids consistently displayed thicker Sr, whereas A and LA hybrids featured a thicker or comparable Cx (Figure 9C).

3.8. Vascular Cylinder

The Vc, situated between the Sr and pith, contained 33 to 164 Vbs per taxon, arranged in two-to-four roughly concentric rows. Peripheral Vbs were embedded in or abutted on sclerenchyma, occasionally extending into the cortex (e.g., ‘Apricot fudge’) (Figure 10). Vbs exhibited U-, V- and I-shaped configurations, with U- and V-shaped being the most ubiquitous (Figure 11A,B). I-shaped Vbs accounted for 40.85% of observations (Figure 11C). Co-xylem strands (containing either fused or separated xylem strands within individual Vb, potentially accompanied by phloem differentiation) within Vbs formed O-, X-, W- and Q-shaped patterns, and were observed occasionally (Figure 11D–G). Separated xylem strands occurred in 56.34% of accessions (Figure 11H,I). Wild species exclusively displayed U- and V-shaped Vbs.
Vbs were collateral, with Xy areas exceeding Ph areas (Xy/Ph ratio = 1.69 to 5.81). Ve dominated Xp in 80.28% of accessions (Ve/Xp ratio ≥ 0.95) and the Xp area exceeded the Ph area in 70.42% (Xp/Ph ratio ≥ 0.95) (Supplementary Table S1). Consequently, Vbs often appeared bicollateral (Figure 11C).
The Vb density ranged from 1.79 per mm2 (‘Abbeville’s pride’) to 6.04 per mm2 (‘Landini’), averaging 2.95 per mm2 (CV = 32.56%). Wild species exhibited significantly higher Vbs densities compared to others groups (p < 0.01, Figure 12A). Individual Vb areas ranged from 0.01 mm2 (‘Landini’) to 0.07 mm2 (‘Beverly Dreams’), averaging at 0.03 mm2 (CV = 29.67%). The majority of accessions exhibited individual Vb areas exceeding the mean value. OT hybrids exhibited significantly larger individual Vb areas compared to A hybrids and wild species (p < 0.01, Figure 12B).
The Bs was composed of Pc and was nearly degraded in the examined cultivars, appearing fragmented on the phloem or on both the phloem and xylem sides, failing to form a complete circle (Figure 13A,B). In contrast, wild species retained a complete circular Bs (Figure 13C).

3.9. Correlation Analysis

Pairwise correlation analysis was performed to elucidate the relationships between the morphological and anatomical indices (Figure 14A, Supplementary Table S2). Streak and projection were inter-related, typically occurring simultaneously (r = 0.83). The Ep L/W ratio was one of the determinants of the Ep shape, which was positively associated (r = 0.86). The Xp/Ph ratio was positively correlated with the Xy/Ph ratio, indicating a larger Xy area correlated with an increased area of Xp (r = 0.89).
The Mantel’s test was employed to analyze the correlation between (1) the lily groups and morphological and anatomical indices, and (2) the bending propensity and morphological and anatomical indices (Figure 14A). A hybrids exhibit a short stature (r = −0.58, p < 0.01). In contrast, O and OT hybrids featured an Ep L/W ratio > 0.95. They exhibited a rectangular or squarish Ep shape (r = 0.51 and 0.53, p < 0.01); meanwhile, OT hybrids had the lowest Cx/Sr ratio (r = −0.57, p < 0.01) and larger individual Vb areas (r = 0.54, p < 0.01) among the examined samples. Wild species were characterized by an intact Bs and a higher Vb density, Xy/Ph ratio and Xp/Ph ratio (r = 0.57, 0.54, 0.52, and 0.66, p < 0.01). Additionally, stem bending was significantly influenced by the individual Vb area and Vb/stem area ratio (Vb/S ratio) (r = −0.62 and −0.53, p < 0.01), but not by the plant height or stem diameter (r = 0.16 and 0.08, p ≥ 0.01) (Supplementary Table S3). Mantel’s test identified anatomical features, such as the Ep shape, Ep L/W ratio, Cx/Sr ratio and Bs integrity, as key identifiers for lily classification, with larger Vb areas positively correlating with stem bending.

3.10. Genetic Relationship Based on 23 Morphological and Anatomical Indices

The genetic relationships among 71 examined samples were elucidated using 23 morphological and anatomical indices and these indices clearly divided the Lilium taxa into two main groups using the ward.D method and Canberra distance (group A and B, Figure 14B). Group A included O and OT hybrids, and group B included A, LA, LO and T hybrids and wild species. Wild species that were historical breeding parents of A hybrids were clustered within group B. Furthermore, three T hybrids and six unidentified cultivars were grouped within group B, although their specific subgroup affiliations remain uncertain. Notably, ‘Mister Sandman’ and ‘Beverly Dreams’ hybrids with bending stems were grouped together in group A.

4. Discussion

4.1. Vascular Bundle Influence Lilium Stem Bending

Stem bending is a critical determinant of the esthetic value and functional performance in ornamental plants. This phenomenon is widely observed across various species, including Lilium cultivars such as ‘Mister Sandman’ and ‘Beverly Dream’, as well as in Pinus [12] and Gerbera [13]. The propensity for stem bending was closely associated with anatomical differences among species, for example, fewer Cx layers or discontinuous Sr rendering stems more prone to bending [14]. Additionally, the number, area and density of Vbs were important factors affecting the bending resistance in peony, with sparsely distributed or smaller-diameter Ve resulting in weaker resistance [15]. In the present study, stem bending in Lilium was strongly correlated with a larger individual Vb area and Vb/S ratio. This finding contradicts previous conclusions in the cultivar ‘Siberia’ [16], which suggested that a larger individual Vb area and Vb/S ratio would enhance the bending resistance by increasing the Vb area, thereby maintaining stem erectness. This mechanism is similar to how plants increase their stem thickness under external pressure to improve the bending strength [17].
Gravitropic analysis revealed that, regardless of the planting orientation, ‘Mister Sandman’ maintained a 60° stem angle, in contrast to ‘Friso’, which achieved vertical orientation through canonical gravitropic correction. This divergence may be attributed to the genetic regulation of cytoskeletal dynamics or cell wall-modifying proteins in ‘Mister Sandman’, which maintain a predetermined growth angle [18]. Further investigation into the ultra-structure of Vb, particularly vessels, during stem development may elucidate cultivar growth patterns.
Moreover, the pronounced development of stem roots in ‘Mister Sandman’ represents another compensatory adaptation. Enhanced adventitious root formation provides mechanical stabilization for obliquely growing stems, potentially compensating for sub-optimal nutrient acquisition due to non-vertical orientation [19].

4.2. Comparison of Stem Anatomical Characteristics Between Lilium and Other Monocots

In this study, an investigation of 71 Lilium accessions revealed a consistent stem anatomical structure characterized by a uniseriate epidermis, continuous Sr and collateral Vb.
The uniseriate epidermis of Lilium aligned with that of most monocots, with an exception of Smilax subsessiliflora, which possessed a biseriate epidermis [20]. The stem Ep shapes were usually rectangular, circular and squarish shape outlines. Notably, in addition to these shapes, jigsaw-puzzle-shaped Ep have been identified for the first time in Lilium, marking the initial report of such shapes in monocots stems. The jigsaw-puzzle-shaped cells on leaf and flower petal surfaces, which have been extensively studied, toughen the protective skin to prevent harmful fissures while facilitating beneficial ones [21]. Similarly, the presence of jigsaw-puzzle-shaped cells in Lilium stems likely confers similar advantages, potentially enhancing stem resilience and resistance to mechanical stress. However, compared to the intricate jigsaw-puzzle cells observed on leaves and petals’ epidermis, those on lily stems are a relatively isometric shape.
Sr shows itself to be highly resistant to compression, tension and bending, providing effective protection to plants. However, the presence of Sr varies among plants, even within the same genus or species. For example, among Scilla taxa from Turkey, Sr was only found in S. autumnalis [22]. In plant stems containing Sr, it can appear as continuous or discontinuous rows. In Smilax species, continuous Sr throughout the stem was unique to S. brasiliensis, S. cissoids and S. rufescens, while the other four species had discontinuous Sr [23]. In this study, all investigated taxa, similar to those in the genus Allium, exhibited continuous Sr [24]. The presence of continuous Sr enables lilies to better adapt to external environmental stresses.
Lilium species typically exhibited collateral Vbs, which were common among monocots and well-suited for terrestrial growth by transporting photosynthates and minerals between leaves and roots. However, Himantoglossum [25] had bicollateral Vbs, while Acorus [26] and Cyperus [27] had amphivasal Vbs. These variations reflected adaptations to different ecological niches, with bicollateral Vbs favoring efficient transport and amphivasal Vbs enhancing water absorption and support in aquatic settings [9].
Stem anatomical persistence is evident in the genus Lilium, yet notable variations exist in the stem shape, the presence of trichome and papillae, the thickness of the cuticle, etc. Previous studies have described these cross-sectional variations, but this research reports novel traits for the first time and represents a comprehensive exploration of the stem anatomy across Lilium taxa.
The cross-section shapes of monocot stems are usually circular, but can vary to triangular, elliptic or polygonal due to genetics, development and mechanical pressure [28]. For example, Gagea pratensis pedicels show triangular, square, or irregular shapes [29]. In a study, 97.18% of lilies had circular or sub-circular stems, with two hybrids showing irregular circular patterns. All wild species had circular stems. The mechanisms behind these variations in lily stem shapes need further study.
The cuticle is crucial for plant–environment interactions, affecting transpiration and protection. Its texture (smooth or situate) can influence water management, pathogen resistance and mechanical properties [30]. In lilies, A, LA and T hybrids had sinuate cuticles, while O, OT and LO hybrids had smooth ones, possibly due to ecological adaptation. For example, A, LA and T hybrids were more suited to the arid climate of northern China [31]. The cuticle thickness varied among plants, with the Allium species having thicker cuticles (7.90 to 39.70 µm) [24] and tulips having thinner ones, except for Tulipa orphanidea (9.50 µm) [32]. In this study, Lilium cuticles were thin (2.65 µm). However, the cuticle thickness was not a significant species identifier due to its sensitivity to environmental changes [24].
Trichomes appear on various plant organs and protect against hazards like herbivores, ultraviolet radiation and water loss. They can be unicellular or multicellular, glandular or non-glandular, and appear as hairs or papillae [33]. In monocots, trichomes are rare. For example, most species in the genera Tulipa, Gagea and Fritillaria have glabrous stems, though a few species like T. orphanidea, G. luteoides and F. aurea have epidermal hairs. In our study, only 28.17% of Lilium taxa had trichomes, which were a unicellular, non-glandular and non-branched type. Other monocots show diverse trichome forms, such as warty trichomes in G. luteoides [34] and capitate glandular trichomes in F. whittallii [35]. Papillae are the localized deposition of cell wall components that function as a defense against penetration [36]. Papillae were also rare in monocots and were mainly found in genera like Fritillaria, Scilla and Iris. In Lilium, only 32.39% of species had papillae.
The statistical analysis showed that the Cx/Sr ratio was ≥ 0.95 in A and LA hybrids, but < 0.95 in OT hybrids. This means that A and LA hybrids had a thicker cortex, while OT hybrids had a thicker Sr. The thick Sr in OT hybrids, which have larger blooms and thicker petals, provides mechanical support. In contrast, the cortex in A and LA hybrids, which are known for their smaller bulbs and numerous small flowers, is important for photosynthesis and for storing water and starch. These anatomical adaptations have also been studied in Poaceae [37].
In Lilium, the outer region has smaller, more frequent Vbs compared to the inner region, consistent with most monocots. Vbs were usually beneath the Sr, but occasionally peripheral Vbs were embedded in the cortex, possibly corresponding to leaf traces, as seen in S. quinquenervia [20]. This pattern of larger inner and smaller outer Vbs was closely related to leaf primordia [38]. In plants like rattan and bamboo, which lack pith and have scattered Vbs beneath the epidermis, this characteristic was used to create functionally graded materials with potential applications in high-tech fields like aerospace [39].
Vb shapes were more diverse in lily hybrids than in wild species. In species, Vbs were mostly V- or U-shaped, similar to those in Fritillaria [40]. This study was the first to find I-shaped and co-xylem Vbs in lilies. Co-xylem Vbs were characterized by increased xylem elements and form shapes like O, X, W and Q, with phloem partitioning. This phenomenon, also called xylem fusion, was rare and was previously only reported in Polygonatum orentale [41].
In Lilium, the Xy/Ph ratio ranged from 1.69 to 5.81 (average 2.65), compared to an average of 1.00 in Fritillaria. Additionally, the Vb density was 1.79 to 6.04 per mm2, the individual Vb area was 0.01 to 0.07 mm2, the Vbs/S ratio was 5.58% to 17.88%, the Ve/Xp ratio was 0.54 to 2.72, and the Xp/Ph ratio was 0.48 to 3.44. These metrics were reported for the first time in Lilium, providing new data for plant anatomy research and insights into the evolution and adaptation of monocots.
In monocots, including Lilium, the Bs usually consisted of a single layer of Pc. However, in Epipremnum aureum, the Bs had two-to-five layers [42]. Sclerenchymatous Bs cells were found in some Poaceae species, as well as in Dioscorea [43]. This sclerenchymatous characteristic was also seen in L. regale, L. polyphyllum [44] and L. ledebourii [45]. While all monocots and Lilium wild species have a fully circular Bs, a degraded Bs has been observed in hybrids. This may reduce intercellular interactions and the metabolic burden, allowing resources to be allocated more efficiently to other vital functions like rapid growth and reproduction [46].
There is confusion about defining pith in monocots. To clarify, we define pith in monocots as the central area without Vbs, following Claßen-Bockhoff et al. [38]. Based on this, we reviewed the available literature on 300 species across 50 monocot genera and developed a classification (Figure 15). Our classification was mainly based on the presence or absence of pith, with further sub-classification into solid or hollow pith for those with pith. Monocot stems lack pith due to widespread Vbs in the ground tissues, like in Iris [47], Dracaena [37], Sorghum [48] and Zea [49] (Figure 15A–D). Epipremnum aureum was special with bifurcated Vbs [42] (Figure 15E). In contrast, most monocots with pith have a central cavity without Vbs, such as Triticum [50], Oryza [51], Hordeum [52] and Bambusa [53] (Figure 15F–I). In the solid pith group, most monocots have parenchymatous pit cells, such as Scilla [22], Fritillaria [40], Polypogon [54] and Ruscus [55] (Figure 15J–M), except for Dioscorea ovata with sclerenchymatous cells [43] (Figure 15N). Lilium belonged to the pith-present group, with most having solid stems. However, four hybrids and one wild species had hollow stems. This variation in stem pith (solid or hollow) was also seen in other genera like Triticum [56].

4.3. Concluding Remarks: Taxonomic Significance of Anatomical Characteristic in Lilium

Recently, many taxonomic viewpoints regarding the classification of members within the genus Lilium have been proposed. The classification of lily hybrids has primarily been based on the parental origin, categorizing them into groups such as A, LA, O, OT, etc., which has been supported by some morphology and molecular studies [5].
Anatomical studies of Lilium stems have provided important taxonomic insights for lily classification, as reported in other monocots plants [57]. However, previous research, mainly for conservation purposes, focused on whole-plant analyses of Lilium species without systematic hybrids classification within the genus.
In contrast, this study systematically analyzed the stem anatomy of various Lilium hybrids, revealing commonalities and differences in anatomical features and identifying traits of significant taxonomic value. The Ep shape, Ep L/W ratio, Cx/Sr ratio and Vb characteristics were identified as distinguishing features between the A/LA hybrids and O/OT hybrids, aligning with the molecular research. The Cx/Sr ratio, which had previously been used to analyze eight Turkish Lilium taxa, was found to significantly differentiate the O/OT hybrids and to classify them into the A/LA hybrids [58]. Wild species exhibit intact sheaths and the highest vascular bundle density, significantly differentiating them from cultivated varieties.
Building on these anatomical insights, future studies should employ multi-omics approaches to functionally validate the bio-mechanical roles of these traits and optimize their application in the molecular breeding of Lilium hybrids with enhanced stem rigidity.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11050546/s1, Table S1: Morphological and anatomical data; Table S2: Correlation data; Table S3: Mantel’s test data.

Author Contributions

F.D. and P.Z. conceived the experiments, K.L. and R.L. collected the samples, K.L. and X.F. conducted the experiments, K.L. and X.F. analyzed the results, K.L. and P.Z. wrote the manuscript, F.D. and N.T. reviewed and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Fundamental Research Program of Shanxi Province (20210302123416) and Laterally-oriented Research Project of Shanxi Agricultural University (2023HX292).

Data Availability Statement

The raw data supporting the conclusions of this manuscript will be made available by the authors, without undue reservation, to any qualified researcher.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Abbreviations

A: Asiatic hybrids; O: Oriental hybrids; T: Trumpet hybrids; LA: Longiflorum × Asiatic hybrids; OT: Oriental × Trumpet hybrids; LO: Longiflorum × Oriental hybrids; W: Wild species; CV: coefficient of variation; Cu: cuticle; Ep: epidermis; Cx: cortex; Sr: sclerenchymatous rings; Vc: vascular cylinder; Vb: vascular bundles; Ve: vessel; Xp: xylem parenchyma; Xy: xylem; Ph: phloem; Bs: bundle sheath; L: length; W: width; Tri.: trichomes; Pap.: papillae; Str. Streak; Pc, parenchymatous cells.

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Figure 1. Schematic diagram of the freehand sectioning experimental procedure.
Figure 1. Schematic diagram of the freehand sectioning experimental procedure.
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Figure 2. Morphological characterization and growth posture in Lilium. Boxplots of plant height (A) and stem diameter (B) for different groups within Lilium. Growth posture of stems in ‘Friso’ and ‘Mister Sandman’: natural images (C) and simulated images (D) from 2023 and 2024. A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
Figure 2. Morphological characterization and growth posture in Lilium. Boxplots of plant height (A) and stem diameter (B) for different groups within Lilium. Growth posture of stems in ‘Friso’ and ‘Mister Sandman’: natural images (C) and simulated images (D) from 2023 and 2024. A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
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Figure 3. Stem cross-sectional shape of Lilium. Circular shape (A) and a magnified view of ‘Mister Sandman’ (B). (C) ‘Orange Cocette’, an irregular shape. (D) ‘Paciano’, hollow cavities in pith region. Ep, epidermal cell; Cx, cortex; Sr, sclerenchymatous ring; Vc, vascular cylinder; Vb, vascular bundle; Ph, phloem; Xy, xylem; Pc, parenchymatous cells. Scale bar: (A,C,D)—1 mm; (B)—100 μm.
Figure 3. Stem cross-sectional shape of Lilium. Circular shape (A) and a magnified view of ‘Mister Sandman’ (B). (C) ‘Orange Cocette’, an irregular shape. (D) ‘Paciano’, hollow cavities in pith region. Ep, epidermal cell; Cx, cortex; Sr, sclerenchymatous ring; Vc, vascular cylinder; Vb, vascular bundle; Ph, phloem; Xy, xylem; Pc, parenchymatous cells. Scale bar: (A,C,D)—1 mm; (B)—100 μm.
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Figure 4. The cuticle features in lily groups. (A) ‘Red Velvet’, sinuate cuticle. (B) ‘Friso’, smooth cuticle. (C) Distribution of cuticle states across lily groups. (D) Boxplots of the cuticle thickness across lily groups. Ep, epidermal cells; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Scale bar: (A,B)—20 μm. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
Figure 4. The cuticle features in lily groups. (A) ‘Red Velvet’, sinuate cuticle. (B) ‘Friso’, smooth cuticle. (C) Distribution of cuticle states across lily groups. (D) Boxplots of the cuticle thickness across lily groups. Ep, epidermal cells; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Scale bar: (A,B)—20 μm. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
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Figure 5. The epidermal cells shapes in lily groups. (A) ‘Conca D’ or squarish. (B) ‘Sweet surrender’, duck-shaped. (C) ‘Pearl Melanie’, crosses-shaped, dumbbell-shaped and horizontal V-shaped. (D) Distribution of four Ep shapes across lily groups. Ep, epidermal cells; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Scale bar: (A–C)—20 μm.
Figure 5. The epidermal cells shapes in lily groups. (A) ‘Conca D’ or squarish. (B) ‘Sweet surrender’, duck-shaped. (C) ‘Pearl Melanie’, crosses-shaped, dumbbell-shaped and horizontal V-shaped. (D) Distribution of four Ep shapes across lily groups. Ep, epidermal cells; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Scale bar: (A–C)—20 μm.
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Figure 6. Trichomes, papillae and stoma. (A) ‘Bazin’, simple hair. (B) ‘Eyeliner’, hair with single basal cell. (C) ‘Forever Susan’, hair with two basal cells. (D) L. lancifolium, multicellular trichome. (E,F) ‘Matrix’, single papillae. (G) ‘Forever Susan’, papillae with basal cell. (H) ‘Bazin’, xerophytic sunken stomata. Ep, epidermal cells. Scale bar: (A–D)—50 μm; (E–H)—20 μm.
Figure 6. Trichomes, papillae and stoma. (A) ‘Bazin’, simple hair. (B) ‘Eyeliner’, hair with single basal cell. (C) ‘Forever Susan’, hair with two basal cells. (D) L. lancifolium, multicellular trichome. (E,F) ‘Matrix’, single papillae. (G) ‘Forever Susan’, papillae with basal cell. (H) ‘Bazin’, xerophytic sunken stomata. Ep, epidermal cells. Scale bar: (A–D)—50 μm; (E–H)—20 μm.
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Figure 7. Distribution of trichomes and papillae across lily groups. (A) Frequency distribution of epidermal appendages: trichome-papillae co-occurrence, exclusive trichomes, exclusive papillae, and absence. (B) Distribution of trichomes across lily groups. (C) Distribution of papillae across lily groups. Tri., trichomes; Pap., papillae; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species.
Figure 7. Distribution of trichomes and papillae across lily groups. (A) Frequency distribution of epidermal appendages: trichome-papillae co-occurrence, exclusive trichomes, exclusive papillae, and absence. (B) Distribution of trichomes across lily groups. (C) Distribution of papillae across lily groups. Tri., trichomes; Pap., papillae; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species.
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Figure 8. Cortical characteristics in lily groups. (A) ‘Sweet Vally’, 4–5 layers of cortical cell arranged tightly. (B) ‘Cali’, 5–6 layers of cortical cell arranged moderately. (C) ‘Corallo Beach’, projection. (D) Distribution of projection across lily groups. Ep, epidermal cells; Cx, cortex; Sr, sclerenchymatous ring; Pro., projection; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Scale bar: (A–C)—100 μm.
Figure 8. Cortical characteristics in lily groups. (A) ‘Sweet Vally’, 4–5 layers of cortical cell arranged tightly. (B) ‘Cali’, 5–6 layers of cortical cell arranged moderately. (C) ‘Corallo Beach’, projection. (D) Distribution of projection across lily groups. Ep, epidermal cells; Cx, cortex; Sr, sclerenchymatous ring; Pro., projection; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Scale bar: (A–C)—100 μm.
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Figure 9. Cortex and sclerenchymatous ring thickness with their ratio in lily groups. Boxplots of the thickness of cortex (A) and sclerenchymatous rings (B) across lily groups. (C) Distribution of Cx/Sr ratio across lily groups. A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
Figure 9. Cortex and sclerenchymatous ring thickness with their ratio in lily groups. Boxplots of the thickness of cortex (A) and sclerenchymatous rings (B) across lily groups. (C) Distribution of Cx/Sr ratio across lily groups. A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
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Figure 10. Distribution of vascular bundles in ‘Apricot Fudge’: overall vascular bundles distribution (A) and magnified view of peripheral vascular bundles extending into the cortex (B). Cx, cortex; Sr; sclerenchymatous rings; Vb, vascular bundles. Scale bar: 1 mm.
Figure 10. Distribution of vascular bundles in ‘Apricot Fudge’: overall vascular bundles distribution (A) and magnified view of peripheral vascular bundles extending into the cortex (B). Cx, cortex; Sr; sclerenchymatous rings; Vb, vascular bundles. Scale bar: 1 mm.
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Figure 11. The various vascular bundles shapes. (A) ‘Mister Sandman’, U-shaped. (B) ‘Mister Sandman’, V-shaped. (C) ‘Corallo Beach’, I-shaped. (D) ‘Mister Sandman’, O-shaped. (E) ‘Sweet Zanica’, X-shaped. (F) ‘Easy Waltz’, W-shaped. (G) ‘Easy Waltz’, Q-shaped. (H) ‘Bright Diamond’, co-xylem consisting of two separated xylems. (I) ‘Easy Waltz’, co-xylem consisting of three separated xylems. Ph, phloem; Ve, vessel; Xp, xylem parenchyma; Xy, xylem. Scale bar: 100 μm.
Figure 11. The various vascular bundles shapes. (A) ‘Mister Sandman’, U-shaped. (B) ‘Mister Sandman’, V-shaped. (C) ‘Corallo Beach’, I-shaped. (D) ‘Mister Sandman’, O-shaped. (E) ‘Sweet Zanica’, X-shaped. (F) ‘Easy Waltz’, W-shaped. (G) ‘Easy Waltz’, Q-shaped. (H) ‘Bright Diamond’, co-xylem consisting of two separated xylems. (I) ‘Easy Waltz’, co-xylem consisting of three separated xylems. Ph, phloem; Ve, vessel; Xp, xylem parenchyma; Xy, xylem. Scale bar: 100 μm.
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Figure 12. Boxplots of the density of vascular bundles (A) and the individual vascular bundles areas (B) across lily groups. A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
Figure 12. Boxplots of the density of vascular bundles (A) and the individual vascular bundles areas (B) across lily groups. A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species. Black dots indicate outliers. Different lowercase letters indicate significant differences (Duncan’s Multiple Range test, p < 0.01).
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Figure 13. The bundle sheath characteristics. (A) ‘Sweet Zanica’, degraded bundle sheath. (B) ‘Tresor’, degraded bundle sheath. (C) L. pumilum, a completely circular bundle sheath. Ph, phloem; Ve, vessel; Xp, xylem parenchyma; Bs, bundle sheath; Pc, parenchymatous cells. Black square-labeled cells: Bs cells. Scale bar: 100 μm.
Figure 13. The bundle sheath characteristics. (A) ‘Sweet Zanica’, degraded bundle sheath. (B) ‘Tresor’, degraded bundle sheath. (C) L. pumilum, a completely circular bundle sheath. Ph, phloem; Ve, vessel; Xp, xylem parenchyma; Bs, bundle sheath; Pc, parenchymatous cells. Black square-labeled cells: Bs cells. Scale bar: 100 μm.
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Figure 14. Correlation and cluster analysis based on 23 indices. (A) Pairwise comparisons of morphological and anatomical characteristics, with a color gradient denoting Pearson’s correlation coefficients. The Mantel’s tests were used to assess the correlations between lily groups, stem susceptibility to bending, and the indices. Edge width corresponds to the Mantel’s r statistic for the corresponding distance correlations. (B) Genetic relationship of 71 lilies based on 23 morphological and anatomical characteristics. A dendrogram was generated using ward.D method and Canberra distance. Group A was highlighted in purple, while group B in green. Cu, cuticle; Ep, epidermal cell; L, length; W, width; Cx, cortex; Sr, sclerenchymatous rings; Bs, bundle sheath; Vb, vascular bundles; S, stem cross-sectional area; Xy, xylem; Ph, phloem; Ve, vessel; Xp, xylem parenchyma; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species.
Figure 14. Correlation and cluster analysis based on 23 indices. (A) Pairwise comparisons of morphological and anatomical characteristics, with a color gradient denoting Pearson’s correlation coefficients. The Mantel’s tests were used to assess the correlations between lily groups, stem susceptibility to bending, and the indices. Edge width corresponds to the Mantel’s r statistic for the corresponding distance correlations. (B) Genetic relationship of 71 lilies based on 23 morphological and anatomical characteristics. A dendrogram was generated using ward.D method and Canberra distance. Group A was highlighted in purple, while group B in green. Cu, cuticle; Ep, epidermal cell; L, length; W, width; Cx, cortex; Sr, sclerenchymatous rings; Bs, bundle sheath; Vb, vascular bundles; S, stem cross-sectional area; Xy, xylem; Ph, phloem; Ve, vessel; Xp, xylem parenchyma; A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species.
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Figure 15. Classification of monocot stem cross-section anatomical characteristics based on within the pith-present group into solid or hollow pith. (A–E), absence of pith. (A) Iris magnifica [47]; (B) Dracaena marginata [37]; (C) Sorghum bicolor [48]; (D) Zea mays [49]; (E) Epipremnum aureum [42]. (F–I), presence of hollow pith. (F) Triticum aestivum [50]; (G) Oryza sativa [51]; (H) Hordeum vulgare [52]; (I) Bambusa vulgaris var. striata [53]. (J–N), presence of solid pith. (J) Scilla bifolia [22]; (K) Fritillaria atrolineata [40]; (L) Polypogon monseplinsis [54]; (M) Ruscus hyrcanus [55]; (N) Dioscorea ovata [43].
Figure 15. Classification of monocot stem cross-section anatomical characteristics based on within the pith-present group into solid or hollow pith. (A–E), absence of pith. (A) Iris magnifica [47]; (B) Dracaena marginata [37]; (C) Sorghum bicolor [48]; (D) Zea mays [49]; (E) Epipremnum aureum [42]. (F–I), presence of hollow pith. (F) Triticum aestivum [50]; (G) Oryza sativa [51]; (H) Hordeum vulgare [52]; (I) Bambusa vulgaris var. striata [53]. (J–N), presence of solid pith. (J) Scilla bifolia [22]; (K) Fritillaria atrolineata [40]; (L) Polypogon monseplinsis [54]; (M) Ruscus hyrcanus [55]; (N) Dioscorea ovata [43].
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Table 1. Lilium taxa used in this study.
Table 1. Lilium taxa used in this study.
No.GroupNameNo.GroupNameNo.GroupName
1AEasy Waltz a25AKesla b49LAEyeliner b
2ALittle Kiss a26AFly 28 b50LASweet Sugar a
3APeach Dwarf a27AFly 9 b51LABright Diamond a
4AAbbeville’s Pride a28A207 b52LAPurple Diamond a
5ATwosome a29A202 b53OTMaldano b
6AForever Susan a30AUnidentified cultivar 1 b54OTProfundo b
7ARed Life a31OSorbonne a55OTConca D’or b
8AAnnemarie’s Dream a32OSiberia a56OTFriso a
9AMatrix a33OTarrango b57OTMister Sandman a
10ASunset Matrix a34OViviana b58OTManissa a
11AGolden Matrix a35TPink Perfection a59OTRobina a
12APearl Melanie a36TOrange Planet a60OTBeverly Dreams a
13ANavona a37TPink Planet a61LOCali b
14ALandini a38LAPavia a62LOWhite Triumph b
15ADiscoteca a39LAPink Brush b63LOVarese b
16ASweet Surrender b40LAEremo b64WL. lancifoliuma
17ASecret Kiss b41LAArmandale b65WL. davidii var. unicolor a
18ARed Velvet b42LABeau Soleil b66WL. pumiluma
19AOrange Cocotte b43LAPaciano b67UKUnidentified cultivar 2 b
20AHeart Strings b44LASweet Zanica b68UKUnidentified cultivar 3 b
21ATresor b45LABrindisi b69UKUnidentified cultivar 4 b
22AFly Tian Cheng b46LAApricot Fudge b70UKUnidentified cultivar 5 b
23AFly Shao Hua b47LACorallo Beach b71UKUnidentified cultivar 6 b
24ABazin b48LASweet Valley b
A, Asiatic hybrids; O, Oriental hybrids; T, Trumpet hybrids; LA, Longiflorum × Asiatic hybrids; OT, Oriental × Trumpet hybrids; LO, Longiflorum × Oriental hybrids; W, wild species; UK, unknown hybrids. a, Accessions were sourced from Baicheng Horticultural Professional Cooperative. b, Accessions were collected from Baguazhou lily experimental base of Nanjing Agricultural University.
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MDPI and ACS Style

Zhou, P.; Liao, K.; Feng, X.; Liang, R.; Teng, N.; Du, F. Morphological and Anatomical Characterization of Stems in Lilium Taxa. Horticulturae 2025, 11, 546. https://doi.org/10.3390/horticulturae11050546

AMA Style

Zhou P, Liao K, Feng X, Liang R, Teng N, Du F. Morphological and Anatomical Characterization of Stems in Lilium Taxa. Horticulturae. 2025; 11(5):546. https://doi.org/10.3390/horticulturae11050546

Chicago/Turabian Style

Zhou, Peng, Kuangkuang Liao, Xiunian Feng, Rui Liang, Nianjun Teng, and Fang Du. 2025. "Morphological and Anatomical Characterization of Stems in Lilium Taxa" Horticulturae 11, no. 5: 546. https://doi.org/10.3390/horticulturae11050546

APA Style

Zhou, P., Liao, K., Feng, X., Liang, R., Teng, N., & Du, F. (2025). Morphological and Anatomical Characterization of Stems in Lilium Taxa. Horticulturae, 11(5), 546. https://doi.org/10.3390/horticulturae11050546

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