Three New Species and a New Record of Murdannia (Commelinaceae) for the Flora of Laos

Abstract

The genus Murdannia Royle was recognized as a member of the family Commelinaceae, known for its beautiful and outstanding flowers, which made it highly valued as an ornamental plant. In this study, three previously unidentified species of Murdannia are described as new species from Laos including Murdannia maronea, M. rhizomatosa, and M. thyrsoidea. Detailed descriptions, illustrations, phenology, and distribution of each species are provided, along with notes on their horticulture. Murdannia clandestina is reported as a new record for Laos. These four species of Murdannia are notable for their attractive flowers, particularly M. thyrsoidea, which was characterized by its large inflorescence, enhancing its potential as an ornamental plant. The pollen morphology of these four Murdannia species is described for the first time. The pollen grains share similar characteristics, being monads, medium-sized, bilaterally symmetrical, and prolate in shape, with a monocolpate aperture and verrucate exine sculpturing. These findings provided valuable insights to support future breeding efforts aimed at enhancing their ornamental value.

1. Introduction

The genus Murdannia Royle is perennial or annual herbs and comprises about 61 species of plants that naturally grow in the tropical and subtropical regions of Africa, Europe, and Asia [1,2,3,4,5]. Murdannia is recognized for their herbaceous and sometimes succulent characteristics. Murdannia plants are commonly found in moist habitats such as wetlands, grasslands, and forest margins. Species in this genus are distinguished by their three petaled flowers, frequently displaying blue or purple shades, and their varied growth forms, which range from creeping to erect [2,3,6,7,8]. In Laos, Murdannia is the largest genus under the Commelinaceae family including 13 species namely Murdannia bracteata (C.B. Clarke) J.K. Morton ex D.Y. Hong, M. edulis (Stokes) Faden, M. gigantea (Vahl) G. Brückn., M. japonica (Thunb.) Faden, M. keisak (Hassk.) Hand.—Mazz., M. macrocarpa D Y. Hong, M. medica (Lour.) D.Y. Hong, M. nudiflora (L.) Brenan, M. simplex (Vahl) Brenan, M. spectabilis (Kurz) Faden, M. spirata (L.) G. Brückn., M. triquetra (Wall. ex C.B.Clarke) G.Brückn., and M. vaginata (L.) G.Brückn [1,9,10,11]. Murdannia is the genus known for its beautiful flowers, with several species cultivated as ornamental plants, including Murdannia gigantea, M. japonica, M. macrocarpa, M. nudiflora, and M. spectabilis [12,13,14,15]. In addition to their ornamental value, some species of Murdannia are also utilized for medicinal purposes. For example, in Champasak Province, Laos, Murdannia japonica is traditionally chewed to strengthen teeth [16].

During a botanical survey in Laos, we identified populations of three previously undescribed species of Murdannia. These new species, named Murdannia maronea Sength., Saensouk, P.Saensouk & Soulad., Murdannia rhizomatosa Sength., Saensouk, P.Saensouk & Soulad., and Murdannia thyrsoidea Sength., Saensouk, P.Saensouk & Soulad., are described in this study. Detailed illustrations and preliminary conservation assessments are also provided for each species. All three new species are notable for their attractive flowers. Additionally, Murdannia maronea and Murdannia thyrsoidea are visually appealing even without flowers due to their large basal rosettes, which make them suitable as ornamental plants for gardens. Furthermore, M. thyrsoidea possesses tubers, while M. rhizomatosa has rhizomes, which may indicate potential medicinal applications, as rhizomatous and tuberous structures in certain Commelinaceae species were reported to contain bioactive compounds with pharmacological significance [17]. However, further phytochemical studies are required to confirm the medicinal potential of this species. In addition, Murdannia clandestina (Ridl.) Faden is reported as a newly recorded species for Laos. This species thrives near streams and shows potential for cultivation in moist environments. The palynological characteristics of the four Murdannia species are described for the first time. Their pollen morphology, documented in detail, provides fundamental information that could support future breeding efforts to enhance their ornamental and horticultural value.

2. Materials and Methods

2.1. Taxonomic Study

Plants in the field were photographed, and various specimens were collected, including dried, living, and those preserved in alcohol. Voucher specimens were deposited in the herbarium of the Faculty of Forest Science at the National University of Laos (FOF) and the herbarium of Mahasarakham University (MSU) in Thailand. Living specimens were cultivated in the nursery of the Walai Rukhavej Botanical Research Institute at Mahasarakham University, Thailand [18]. Type specimens of morphologically similar species were compared and verified using digital images available online, as well as all published literature on Murdannia, and examined under a stereoscopic microscope. A preliminary conservation assessment was conducted based on the IUCN Red List categories [19].

2.2. Palynological Study

The inflorescences of all species in the field were collected and the samples were preserved in 70% alcohol. The anthers were removed from the flowers and the samples were dehydrate using alcohol series as follows: 70%, 90%, 95%, and 100%.

The pollen samples were divided into two parts; the first part was examined by using Light Microscopy (LM). Briefly, 30 pollen grains of each specimen were used to measure the polar axis (P), equatorial diameter (E), and exine thickness. They were then photographed using LM (Axiostar plus, C. ZEISS, Oberkochen, Germany). The second part was examined by using Scanning Electron Microscopy (SEM), where the pollen grains were suspended in absolute alcohol. Then, the pollen grains were dried and attached to aluminum stubs with double-sided cellophane tape and coated with gold. The micrographs were taken using an SEM (Hitachi, TM–4000plus, Chiba, Japan) to determine the details of the exine sculpturing and aperture structure. The terminology classes followed a Glossary of pollen and spore terminology [20,21]. Pollen shape classification followed a book on pollen and spore terminology [22,23] based on the P/E ratio.

Using a light microscope (LM) for collecting data of Commelinaceae, including pollen size, shape, and ornamentation, the shape and size were measured on the dorsal side. These were studied at the laboratory of Walai Rukhavej Botanical Research, Mahasarakham University in Thailand.

Using a Scanning Electron Microscope (SEM) for collecting data of Commelinaceae pollen including ornamentation of sulcus and ornamentation of tectum, photomicrographs measured on the dorsal side. These were studied at Laboratory Equipment Center, Mahasarakham University, Thailand.

3. Results

3.1. Taxonomic Treatments

Murdannia maronea Sength., Saensouk, and P.Saensouk & Soulad. sp. nov. are shown in Figure 1 and Figure 2.

Type: Laos. Southern—Champasak Province, 16 June 2023, Sengthong A, et al., AS329 (Holotype FOF!; isotypes Mahasarakham University Herbarium (MSU!)).

Perennial herbs, with basal rosettes with spirally arranged leaves. Roots are moderately thick ca. 0.5 cm, rhizome absent. Leaves of basal rosette, elliptic–ovate 20–45 × 4.5–7.5 cm, glabrous, base cuneate, apex acute to acuminate, margins thickened hyaline or maroon, undulate. Flowering shoot: Three to six per plant, subscapiform terminal on the rosette, solitary, unbranched, 30–50 cm long without leaves. Inflorescences: Mainly axillary, consisting of two to five bladeless sheaths, each ca. 1.5 cm long, closely fitting the stem, not or only the upper two overlapping, glabrous, each bladeless sheath partially enclosing an axillary fascicle of cincinni; cincinni up to five flowers, typically one-noded, the basal node persistent, ca. 7 mm long; bracteoles membranous, elliptic-ovate, 2.5–5.5 × 1.5–2 mm, perfoliate, glabrous. Flowers actinomorphic, maroon; pedicels short, less than 2 mm long, usually sparsely glandular-puberulous. Sepals: Green often with maroon, lanceolate, 3.5–5 × 1.5–3 mm, usually glandular puberulous outside. Petals maroon, elliptic obovate, ca. 5 × 4.5 mm. Fertile stamens: Three, filaments ca. 3 mm long, violet-bearded, anthers violet, elliptic-oblong, ca. 1 × 0.5 mm. Staminodes: Three, filaments ca. 2 mm long, bearded, antherodes white-creamy, hastate, ca. 1 × 0.9 mm. Ovary: Ellipsoid, 0.8–2 × 0.4–1 mm, glabrous, styles 3–4.5 mm long, stigma simple.

Distribution: Laos, Champasak Province, Sanasomboun District, Nong Phai village; Thailand, Ubon Ratchathani province.

Ecology: On rocks, wet places in deciduous forest, alt. 250 m; flowering from June to August; daily flowering time in late afternoon to evening.

Vernacular name: Van-Kap-Deng.

Etymology: The specific epithet “maronea” is derived from marron, the French word for “chestnut”, referring to the maroon coloration observed in leaf margins, cincinni, and petals.

Additional specimens examine (paratypes): Thailand, Ubon Ratchathani, Pho Sai, 22 August 2023, Sengthong A, et al., AS441 (MSU, FOF).

Note: This species produces inflorescences that arise from a basal rosette. The number of inflorescences is influenced by the size of the basal rosette, which varies based on the growing substrate. Plants growing on rocks or limestone with sufficient moisture tend to develop larger basal rosettes and produce more inflorescences compared to those growing in soil.

Murdannia rhizomatosa Sength., Saensouk, and P.Saensouk & Soulad. sp. nov. are shown in Figure 3 and Figure 4.

Type: Laos. Southern—Champasak Province, 24 July 2023, Sengthong A, et al., AS402 (Holotype FOF!; isotypes Mahasarakham University Herbarium (MSU!)).

Perennial herbs, with basal rosettes with spirally arranged leaves, ascending. Roots are thin, rhizome horizontal. Leaves are linear 30–45 × 0.3–0.5 cm, pubescent, apex acute to acuminate, margins thickened, revolute, base maroon, mouth ciliate. Flowering shoot: Four to seven per plant, subscapiform terminal on the rhizome, ascending, branched 1 (-2), congested at the top. Inflorescences: Compound, terminal on flowering shoot, and often axillary from the uppermost bract, leaf sheaths on flowering shoots, ca. 3 × 1.5 mm, pubescent, mouth ciliate, each inflorescence often consisting of numerous elongate cincinni, zigzag; cincinni 5.5–7.5 cm long, many-flowered with prominent secund floral scars, cincinnus bracts amplexicaul, lanceolate-ovate, ca. 2 × 1.5 mm, cincinnus peduncles 2–3.5 cm long; bracteoles translucent green, broadly ovate-ovoid, 1.3–2 × 0.6–1 mm, glabrous, caducous. Flowers: White, bisexual, zygomorphic, producing much mucilage in buds; pedicels ca. 2 mm long. Sepals: Green, lanceolate, 2.5–4.5 × 1.5–2.5 mm, glabrous. Petals: White, oblanceolate-obovate, 3–4.5 × 2–3.5 mm. Fertile stamens: Two, filaments ca. 4 mm long, densely pale white-creamy, bearded on lower-middle part, anthers white-creamy, ellipsoid-oblong, ca. 1.5× 0.7 mm. Staminodes: Three, the with filaments 3 mm long, creamy-yellow, bearded on middle to lover part, antherodes hastate, dull yellow, ca. 1 × 0.7 mm. Ovary: Ellipsoid-ovoid, ca. 1.5 × 1 mm, styles ca. 4 mm long, stigma simple.

Distribution: Laos, Champasak Province, Paksong District, Nong Luang village.

Ecology: Wet places in open area neary stream, alt. 550 m; flowering from June to August; daily flowering time in late afternoon to evening.

Vernacular name: Van-Khow-Noy.

Etymology: The specific epithet “rhizomatosa” is derived from the Latin word rhizomatosus, -a, -um, meaning “having a rhizome”, referring to the plant’s well developed rhizomatous growth habit.

Note: This species exhibits an ascending growth habit and thrives better when cultivated in soil compared to pots. Under suitable conditions, it takes less than two years to develop rhizomes.

Murdannia thyrsoidea Sength., Saensouk, and P.Saensouk & Soulad. sp. nov. are shown in Figure 5 and Figure 6.

Type: Laos. Southern—Champasak Province, 14 June 2023, Sengthong A, et al., ANS319 (Holotype FOF!; isotypes Mahasarakham University Herbarium (MSU!)).

Perennial herbs, basal rosettes with spirally arranged leaves. Roots are moderately thick, with distal tuberous roots to ca. 1.5 cm in diam., rhizomes absent. Leaves of basal rosette, linear-lanceolate 20–60 × 3.5–7 cm, glabrescent, apex acuminate, margins cartilaginous, undulate. Flowering shoot: Two up to five per plant, lateral, from basal rosette leaves, erect, up to ca. 1 m long, unbranched, leaf sheaths on flowering shoots, 2–7 × 0.5–1.5 cm, pubescent, mouth ciliate, leaves on flowering shoot several, distichous, lanceolate-ovate, 4.5–9.5 × 1–2.5 cm, leaf sheaths, 2.5–4.5 × 0.5–1.5 cm, base rounded, amplexicaul, apex acute, margins cartilaginous, glabrescent, ciliate basally. Inflorescences: Panicles terminal, compound, lax thyrses, terminal on flowering shoots, with numerous alternates, elongate, ascending or deflexed cincinni, secondary inflorescence frequently reproduced from axils of the lower cincinnus bracts, consisting of 1–4 cincinni, inflorescent bracts 5–12 × 2.5–4.5 cm, sheathing at the base, persistent, secondary, inflorescence axes 13–25 cm long, zigzag, cincinni 1.5–6 cm long, cincinnus axes, 1–4.5 cm long, often with 7–15 flowers, cincinnus bracts membranous, perfoliate, lanceolate-ovate, 2.5–12 × 3.5–10 mm, glabrous, often green marked with maroon, caducous, cincinnus peduncle 0.7–3.5 cm long, bracteoles membranous, often translucent green with maroon, ovate, perfoliate, 1.7–4.5 × 1.5–4.5 mm, glabrous. Flowers: Actinomorphic, white, pedicels straight to ascending, 5–10 mm long, often creamy, glabrous. Sepals: Often translucent white-creamy, lanceolate-ovate, 5.5–9 × 2.5–4.5 mm, boat-shaped, glabrous, apex acute, with three ridges and two grooves outside. Petals: White, broadly obovate-suborbicular, 6–9 × 5–7 mm. Fertile stamens: Three, filaments 3.5–5.5 mm long, white, bearded on lover part, anthers yellow, ovoid, 2.5–4.5 × 0.7–1.5 mm. Staminodes: Three, filaments 2.5–3.5 mm long, bearded, antherodes yellow, trilobed, 1–3 × 1–3 mm. Ovary: White or green, ellipsoid-ovoid, 1–2.5 × 0.8–1.5 mm, styles white, 2–5.5 mm long, stigma simple.

Distribution: Laos, Champasak Province, Sanasomboun District.

Ecology: In the gallery forest, wet places in deciduous forest, alt. 150 m; flowering from June to August; daily flowering time in late afternoon to evening.

Vernacular name: Van-Dork-Khoaw.

Etymology: The specific epithet “thyrsoidea” is derived from the Latin thyrsoideus, -a, -um, meaning “resembling a thyrse,” referring to the plant’s inflorescence, which is arranged in a thyrse—a compact, branched, and often pyramidal flower cluster.

Note: This species produces inflorescences that arise from a basal rosette. The size of the inflorescences depends on the size of the leaves; larger leaves result in larger inflorescences. The size of the leaves, in turn, is influenced by the planting conditions. When grown in pots, the leaf size is proportional to the size of the pot, with larger pots allowing for larger leaves. However, plants grown directly in the soil tend to develop larger leaves compared to those grown in pots. Leaf size is also affected by the moisture availability at the planting site.

Murdannia clandestina (Ridl.) Faden in Smithsonian Contr. Bot. 76: 152. 1991.

Type: Malaysia, Perak, H.N. Ridley 14352 (holotype K!, isotype SING! Digital image).

Distribution: Malaysia, Thailand, Laos.

Ecology: Growing by edge of stream in gallery forest, alt. ca. 1100 m.

Phenology: Flowering and fruiting specimens were collected in October.

Specimens examined: Houaphan Province [Hiew District, Nam Phoung Village, 1100 m, 17 October 2023, Sengthong et al. AS406 (FOF)] (Figure 7).

Note: This species grows well in areas with sufficient moisture and helps cover the soil, aiding in moisture retention.

3.2. Palynology of Murdannia

The pollen morphology of the four species of Murdannia were observed and analyzed under LM and SEM. The results show that the pollen grains in four species of Murdannia are single, heteropolar, and monosulcate. The proximal face of the grains is straight, and in some species displays a slight ridge. The sulcus extends along the convex distal face between the equatorial axes, i.e., it is anasulcate. The information about each species is described as follows:

• Murdannia clandestina

The pollen is monad, medium-sized, has bilateral symmetry, prolate shape, monocolpate aperture, and verrucate in exine sculpturing. The polar axis (P) ranged from 33.12 to 35.97 (34.77 ± 0.82) µm. The equatorial diameter (E) ranged from 18.21 to 21.34 (19.66 ± 0.73) µm. The exine thickness of the pollen ranged from 0.49 to 0.68 (0.52 ± 0.04) µm. Spinulae length ranged from 0.45 to 0.82 (0.48 ± 0.09) µm. Spinulae height ranged from 0.10 to 0.34 (0.23 ± 0.06) µm (Figure 8a–c).

• Murdannia maronea

The pollen is monad, medium-sized, has bilateral symmetry, prolate shape, monocolpate aperture, and verrucate in exine sculpturing. The polar axis (P) ranged from 32.25 to 35.46 (34.65 ± 0.65) µm. The equatorial diameter (E) ranged from 17.76 to 20.55 (19.42 ± 0.83) µm. The exine thickness of the pollen ranged from 0.40 to 0.78 (0.52 ± 0.04) µm. Spinulae length ranged from 0.23 to 0.62 (0.45 ± 0.08) µm. Spinulae height ranged from 0.15 to 0.44 (0.26 ± 0.07) µm (Figure 8d–f).

• Murdannia rhizomatosa

The pollen is monad, medium-sized, has bilateral symmetry, prolate shape, monocolpate aperture, and verrucate in exine sculpturing. The polar axis (P) ranged from 25.45 to 29.55 (28.29 ± 0.79) µm. The equatorial diameter (E) ranged from 15.78 to 18.75 (17.42 ± 0.76) µm. The exine thickness of the pollen ranged from 0.41 to 0.63 (0.50 ± 0.05) µm. Spinulae length ranged from 0.30 to 0.57 (0.47 ± 0.08) µm. Spinulae height ranged from 0.10 to 0.33 (0.24 ± 0.08) µm (Figure 8g–i).

• Murdannia thyrsoidea

The pollen is monad, medium-sized, has bilateral symmetry, prolate shape, monocolpate aperture, and verrucate in exine sculpturing. The polar axis (P) ranged from 36.78 to 40.29 (39.34 ± 0.88) µm. The equatorial diameter (E) ranged from 19.57 to 23.55 (22.07 ± 0.64) µm. The exine thickness of the pollen ranged from 0.47 to 0.62 (0.52 ± 0.03) µm. Spinulae length ranged from 0.32 to 0.65 (0.50 ± 0.08) µm. Spinulae height ranged from 0.14 to 0.36 (0.25 ± 0.06) µm (Figure 8j–l).

Key to species
1a. Plants with rhizome	2
1b. Plant without rhizome	7
2a. Inflorescences shoot from rhizome	M. rhizomatosa
2b. Inflorescences shoot from the stem	3
3a. Main stem undeveloped	M. bracteata
3b. Main stem developed	4
4a. Antherodes 3-sect; panicles terminal	5
4b. Antherodes sagittate; flowers 1–5 in fascicles in leaf axils	6
5a. Involucral bracts sheathlike, with several to numerous 1-flowered cymes	M. vaginata
5b. Involucral bracts not sheathlike, cymes not 1-flowered	M. spirata
6a. Capsule oblong, trigonous	M. triquetra
6b. Capsule long ellipsoid, obscurely trigonous	M. keisak
7a. Plants with basal rosette	8
7b. Plants without basal rosette	15
8a. Flowering shoot terminal, central in the rosette	9
8b. Flowering shoot axillary from the rosette leaves	12
9a. Cincinni composed of dense secund flowers	10
9b. Cincinni and flowers not as above	11
10a. Sepal less than 8.5 mm long	M. macrocarpa
10b. Sepal more than 8.5 mm long	M. gigantea
11a. Leaves less than 10 mm wide, tubular sheathing bracts glabrous	M. medica
11b. Leaves more than 10 mm wide, tubular sheathing bracts puberulent	M. spectabilis
12a. Flowering shoots with well-developed leaves	M. japonica
12b. Flowering shoots with bladeless sheathing bracts	13
13a. Inflorescence axillary	M. maronea
13b. Inflorescence terminal or lax thyrses	14
14a. Flowering shoot without leaves	M. edulis
14b. Flowering shoot with several leaves	M. thyrsoidea
15a. Plants ascending to erect	M. clandestina
15b. Plants diffuse or spreading decumbent	16
16a. Flowers dense on the cincinnus	M. nudiflora
16b. Flowers pendulous in bud	M. simplex

4. Discussion

This research describes three new species of Murdannia: Murdannia maronea, which has a distinct maroon color clearly visible on its leaf margins, peduncles, and petals; Murdannia rhizomatosa, characterized by an inflorescence shoot that arises from a rhizome, a unique structure and a specific feature of this species; and Murdannia thyrsoidea, notable for having the largest leaves and inflorescences among Murdannia species, with numerous white flowers in the inflorescences. Additionally, we report a newly recorded species of Murdannia, Murdannia clandestina, previously known only from Malaysia, Thailand, and Laos. These four species are admired for their beautiful flowers and can be easily cultivated as ornamental plants in gardens. For example, M. nudiflora, commonly known as doveweed, is prevalent in Florida landscapes and nurseries, indicating its adaptability to cultivated settings [14]. Moreover, cultivating these species can aid in preserving genetic diversity and protecting them from habitat loss. Murdannia can be propagated through seed propagation, stem cuttings or layering, and rhizome or tuber division, all of which allow them to grow well in gardens. Murdannia maronea and M. thyrsoidea, which have large basal rosettes, remain attractive even without flowers. Meanwhile, Murdannia clandestina grows well and can cover the soil surface, making it a good choice for creating green areas in gardens. The key to successfully cultivating these species is ensuring they receive adequate water, as they thrive in moist environments. Additionally, Murdannia thyrsoidea has tubers and M. rhizomatosa has rhizomes, both of which may have potential medicinal uses pending further chemical investigations.

The pollen morphology of the four Murdannia species is described as single, heteropolar, and monosulcate, as is consistent in size and shape with previous studies [17,18]. This represents a new documentation of the pollen morphology for these species. This information provides a foundation for future studies on the breeding and reproduction of these species, which could lead to the development of more prominent inflorescences and enhance their ornamental value.

Provisional Conservation Status: As these are newly identified species, including M. maronea, M. rhizomatosa, and M. thyrsoidea, further observation and sampling are needed to assess their distribution and population size in different areas. Due to the limited data currently available, it is suggested that these species be classified as “Data Deficient” (DD) under the IUCN Red List criteria (IUCN Standards and Petitions Subcommittee, 2024). This classification highlights the need for more comprehensive studies before a conclusive risk status can be determined, as insufficient data are a common factor for all newly discovered species. For these new species, we have made this decision not to publish the precise location to avoid indiscriminate collection that could put the species at risk. Our choice is based on the intention to prevent over-collection and protect the species from potential harm.