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Research Article
Three new species of Elatostema (Urticaceae) from Thailand
expand article infoNatthawut Triyutthachai, Long-Fei Fu§, Pramote Triboun|, Yi-Gang Wei§, Pimwadee Pornpongrungrueng
‡ Khon Kaen University, Khon Kaen, Thailand
§ Guangxi Institute of Botany, Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences, Guilin, China
| National Biobank of Thailand, National Science and Technology Development Agency, Thailand Science Park, Pathum Thani, Thailand
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Abstract

Three new species of Elatostema (Urticaceae) from Thailand, E. kaweesakii Triyutth. & L.F.Fu, sp. nov., E. rubricaule Triyutth. & L.F.Fu, sp. nov. and E. saxatile Triyutth. & L.F.Fu, sp. nov., are newly described and illustrated. These new species can be distinguished by the presence of rhizome. Elatostema kaweesakii is similar to E. atroviride. Elatostema kaweesakii is a lithophyte growing in limestone crevices. It differs from E. atroviride by its large swollen rhizome, glabrous stem, glabrous receptacle, number of tepal in staminate flower, absence of tepal in pistillate flower, presence of staminodes in pistillate flower and smooth achene. Elatostema rubricaule and E. saxatile are found on sandstone habitats. They have distinct flattened and disk-like rhizome. Elatostema rubricaule is distinguished by its distinct sulcate and reddish stem with flattened and disc-like rhizome and chartaceous leaves with entire margin. Elatostema saxatile resembles E. bulbiferum but differs by its flattened and disc-like rhizome, acute leaf apex, glabrous receptacle in pistillate inflorescences, presence of staminodes in pistillate flower, and its sandstone habitat. Descriptions, distribution, ecological and phenological data are provided.

Keywords

Flora of Thailand, limestone, nettle family, rhizomatous plant, Rosales, sandstone, taxonomy

Introduction

Elatostema J.R. Forst. & G. Forst. is a large genus of Urticaceae containing several hundred species distributed throughout tropical and subtropical Asia (Christenhusz et al. 2017; Fu et al. 2021). Elatostema is a succulent herb normally found in evergreen forest, along stream, gorges, caves and limestone mountains (Wang 2014; Fu et al. 2017; Monro et al. 2018). Based on molecular and morphological evidences, a recent systematic study (Tseng et al. 2019) demonstrated that Elatostema is a monophyletic genus that includes Pellionia Gaudich.

The first checklist of Elatostema (including Pellionia) in Thailand documented 14 species (Yahara 1984). Since then, 20 species of Elatostema (including Pellionia) were listed by Pooma and Suddee (2014). However, a recent study involving extensive investigations has resulted in 75 species of Elatostema in Vietnam (Fu et al. 2019), which doubles the number of species in the previous checklist (Hiep 2005). This suggests that the species diversity documentation in Thailand was out of date due to its under-sampled status (Middleton et al. 2019).

As part of ongoing research into the flora of Thailand, the authors undertook extensive field investigations and collected three unknown specimens of Elatostema from the northeastern region of Thailand. After a careful comparison among specimens, it was clear that these specimens belong to the clade that includes Pellionia and Elatostema in Tseng et al. (2019), but they were distinct from other species of this clade. Therefore, we confirmed them as three new species of Elatostema.

Materials and methods

Between 2016 and 2022, the authors conducted several field trips throughout Thailand. The herbarium collections from AAU, BCU, BK, BKF, C, HNU, IBK, K, L, KKU, P, PSU, QBG and SING (Thiers 2022) were examined mainly by the first author. All morphological characters were measured and compared based on dried specimens from field and herbarium collections.

Taxonomic treatment

Elatostema kaweesakii Triyutth. & L.F.Fu, sp. nov.

Figs 1, 2

Diagnosis

Elatostema kaweesakii is similar to E. atroviride W.T. Wang but differed by its large swollen rhizome, staminate inflorescences with 2–7 cm long peduncle, receptacle rectangular, glabrous, staminate flower with 5 ovate tepals, pistillate inflorescences with 5–10 mm long peduncle, receptacle rectangular, glabrous, pistillate flower without tepals, staminode present and achene smooth (Table 1).

Table 1.

Comparison of Elatostema atroviride, E. bulbiferum, E. kaweesakii, E. rubricaule and E. saxatile.

Characters E. atroviride E. kaweesakii E. rubricaule E. saxatile E. bulbiferum
Habitat lithophyte in limestone soils lithophyte in limestone crevices lithophyte on sandstone rocks lithophyte on sandstone rocks lithophyte in limestone crevices
Rhizome slender rhizome or stoloniferous large swollen rounded rhizome flattened, disk-like rhizome flattened, disk-like rhizome swollen rounded rhizome
Stem Simple or branched, greenish, pubescent Simple or branched, greenish, glabrous Simple, reddish, glabrous Simple or branched, greenish, glabrous Simple or branched, greenish, glabrous
Nanophyll absent absent absent present present
Leaf margin dentate serrate to dentate entire serrate serrate
Leaf apex acuminate acuminate obtuse acute acuminate to caudate
Staminate inflorescences: type Capitate Capitate Umbellate Umbellate Umbellate
Staminate inflorescences: receptacle elliptic, chartaceous, pubescent rectangular, chartaceous, glabrous absent absent absent
Staminate inflorescences: peduncle 2–5 mm long 2–7 cm long 2– 3 cm long 1–5 cm long 2–5 cm long
Staminate flower: tepal number 4 5 5 5 5
Pistillate inflorescences: type capitate capitate capitate capitate capitate
Pistillate inflorescences: receptacle oblong, membranous, pubescent rectangular, chartaceous, glabrous elliptic, membranous, glabrous elliptic, membranous, glabrous elliptic, membranous, pubescent
Pistillate inflorescences: peduncle 2–4 mm long, glabrous 5–10 mm long, glabrous sessile to subsessile, glabrous 0.5–5 mm long, glabrous 0–2 mm long, glabrous
Pistillate flower: tepal number 3 absent 5 5 5
Pistillate flower: staminode absent 3 5 5 absent
Achene 6–8 ribbed smooth smooth smooth smooth

Type

Thailand. Loei: Nong Hin district, 17°7.3'N, 101°56.05'E, 360 m alt., 9 August 2022, Triyutth. 332 (holotype KKU!; isotypes AAU!, BKF!).

Description

Perennial herbs, lithophytic, monoecious, rhizomatous. Rhizome rounded, 2–20 cm in diam., brownish. Stems 15–50 cm tall, simple or branched, succulent, greenish, glabrous. Stipules 2, persistent or sometimes caducous in reproductive stage, linear or lanceolate, 4–7 × 1–3 mm, membranous, glabrous. Nanophylls absent. Leaves distichous, alternate; petiole 0.5–1 cm long, greenish, glabrous; lamina asymmetrically ovate to elliptic, 5–20 × 3–10 cm, base oblique, margin serrate to dentate, apex acuminate, chartaceous; venation pinnate, major basal lateral veins present; upper and lower surfaces greenish, glabrous, cystoliths fusiform, 0.2–0.5 mm long. Staminate inflorescences axillary, solitary, capitate, 1.5–2.0 cm in diam.; peduncle 2–7 cm long, glabrous or pubescent; receptacle rectangular, 0.6–1.0 × 0.6–1.0 cm, chartaceous, glabrous; bracts ovate, connate at base, membranous, glabrous; bracteoles lanceolate, 0.6–0.8 × 0.2–0.3 mm, membranous, pubescent. Staminate flowers 80–100 per inflorescence, sessile to subsessile, glabrous; tepals 5, ovate, 1.0–1.5 × 1.0–1.5 mm, apex acuminate, membranous, pubescent; stamens 5, filaments 1.0–1.5 mm long, anthers 0.6–0.8 mm long. Pistillate inflorescences axillary, solitary, capitate 5–10 mm in diam., peduncle 0.5–1.0 cm long, glabrous; receptacle rectangular, 6–8 × 6–8 mm, chartaceous, glabrous; bracts ovate, 0.8–1.0 × 0.5–0.6 mm, membranous, pubescent; bracteoles lanceolate, 0.4–0.6 × 0.2–0.3 mm, membranous, pubescent. Pistillate flowers 40–100 per inflorescence, sessile to subsessile, glabrous; tepals absent; staminodes 3, oblong to linear, 0.2–0.3 mm long; ovary superior, ovoid, 0.3–0.5 mm long. Achenes ellipsoid, 0.8–1.2 mm long, brownish, smooth.

Distribution

Currently known only from Loei province in northeastern Thailand.

Ecology

Occur in limestone crevices.

Phenology

Flowering and fruiting in April–December.

Etymology

This species is named in honor of Mr Kaweesak Keeratikiat, who first discovered the plants.

Conservation status

This species was found in fewer than 5 locations at Nong Hin district, Loei province, Thailand. Moreover, it has a very small population and very restricted distribution, and the number of mature individuals is fewer than 250. According to IUCN (2022) this species should be assessed as Endangered (EN) under IUCN criteria B2a and D1.

Additional specimens examined

Thailand. Loei: Nong Hin district, 16 December 2013, S. Saengvirotjanapat 635 (QBG!), ibid., 20 April 2021, Triyutth. 329 (KKU!).

Notes

This species is similar to E. atroviride in their habitat as lithophytes growing in limestone crevices. Both species have rounded rhizome, absence of nanophyll and a similar shape of leaves. However, it differs from E. atroviride by several characters such as its large rounded rhizome (small size of rhizome in E. atroviride), staminate inflorescences with 2–7 cm long peduncle (vs 2–5 mm long), receptacle rectangular and glabrous (vs elliptic and pubescent), staminate flower with 5 tepals (vs 4 tepals), pistillate inflorescence with 5–10 mm long peduncle (vs 2–4 mm long), absence of tepals in pistillate flower (vs 3 tepals), 3 staminodes (vs staminode absent) and achene smooth (vs 6–8 ribbed).

Figure 1. 

Elatostema kaweesakii Triyutth. & L.F.Fu, sp. nov. A habit B staminate inflorescence C staminate flower D pistillate inflorescence E pistillate flower F bracteole G achene (Drawn by N. Triyutthachai).

Figure 2. 

Elatostema kaweesakii Triyutth. & L.F.Fu, sp. nov. A habit and habitat B pistillate inflorescence C staminate inflorescences (Photos A, C by K. Keeratikiat, B by Triyutth).

Elatostema rubricaule Triyutth. & L.F.Fu, sp. nov.

Figs 3, 4

Diagnosis

Elatostema rubricaule differs from other Thai Elatostema by its distinct sulcate and reddish stem with flattened and disk-like rhizome and chartaceous leaves with entire margin. It grows on seasonally moist sandstone rock (Table 1).

Type

Thailand. Buengkan: Wat A-Hong Silawas, 18°25.47'N, 103°28.2'E, 160 m alt., 13 September 2017, Triyutth. 201 (holotype KKU!; isotypes AAU!, BKF!, IBK!, K!).

Description

Perennial herbs, lithophytic, monoecious, rhizomatous. Rhizome flattened, disk-like, 1–3 cm in diam., brownish. Stems 5–25 cm tall, simple, sulcate, succulent, reddish, glabrous. Stipules 2, persistent or sometimes caducous in reproductive stage, linear or lanceolate, 2.0–2.5 × 0.5–1.5 mm, membranous, glabrous. Nanophylls absent. Leaves distichous, alternate; petiole 0.5–2.0 mm long, reddish, glabrous; lamina asymmetrically lanceolate to elliptic, 3–5 × 0.5–1.5 cm, base asymmetrical attenuate, margin entire, apex obtuse, chartaceous; venation pinnate, major basal lateral veins absent, lateral veins 5–7 pairs; upper surface greenish, glabrous, cystolith fusiform, 0.2–0.5 mm long; lower surface cinereous, glabrous, cystoliths fusiform, 0.2–0.5 mm long. Staminate inflorescences axillary, solitary, umbellate; peduncle 2–3 cm long, glabrous; receptacle absent; bracts lanceolate, 0.8–1.0 × 0.3–0.5 mm, membranous, pubescent; bracteoles lanceolate, 0.6–0.8 × 0.2–0.3 mm, membranous, pubescent. Staminate flowers 5–10 per inflorescence; pedicel 1–3 mm long, glabrous; tepals 5, ovate to oblong, 1.0–1.5 × 1.0–1.5 mm, apex obtuse, membranous, glabrous; stamens 5, filaments 1.5–2.0 mm long, anthers 0.6–1.0 mm long. Pistillate inflorescences axillary, solitary, capitate 5–8 mm in diam., sessile to subsessile, glabrous; receptacle elliptic, 2.0–2.5 × 1.0–1.5 mm, membranous, glabrous; bracts lanceolate, 0.4–0.6 × 0.2–0.3 mm, membranous, pubescent; bracteoles lanceolate, 0.3–0.4 × 0.2–0.3 mm, membranous, pubescent. Pistillate flowers 50–80 per inflorescence; pedicel 0.5–1.0 mm long, glabrous; tepals 5, lanceolate to oblong, 0.8–1.2 × 0.2–0.4 mm, membranous, pubescent; staminodes 5, linear, 0.2–0.4 × 0.1–0.2 mm; ovary superior, ovoid, 0.3–0.5 mm long. Achenes ellipsoid, 0.5–0.8 mm long, brownish, smooth.

Figure 3. 

Elatostema rubricaule Triyutth. & L.F.Fu, sp. nov. A habit B staminate inflorescence C pistillate inflorescences D pistillate flower E bracteole F achene (Drawn by Triyutth).

Figure 4. 

Elatostema rubricaule Triyutth. & L.F.Fu, sp. nov. A habit and habitat B pistillate inflorescences C staminate inflorescence (Photos by Triyutth).

Distribution

Currently known only from the type locality in northeastern Thailand.

Ecology

Occurs on seasonal moist sandstone rocks in shaded areas.

Phenology

Flowering and fruiting in July–October.

Etymology

Latin ruber, red, and caulus, stem, alluding to stem color of the new species.

Conservation status

Elatostema rubricaule is currently known only from the type locality, which is not a protected area, and the number of mature individuals is fewer than 1,000. According to IUCN (2022), this species should be assessed as Critically Endangered (CR) according to criteria B1a, B2a and D1.

Additional specimens examined

Thailand. Buengkan: Wat A-Hong Silawas, 18°25.47'N, 103°28.2'E, 160 m alt., 28 April 2018, Triyutth. 269 (KKU!).

Notes

This species differs from other Thai Elatostema by its habitat. Most species of Elatostema are dwelling on limestone, stream bank, gorges and caves in evergreen forest, but E. rubricaule was found on moist sandstone rocks near the bank of Mekong River in Buengkan Province in the northeastern part of Thailand. The most distinguished characters of this species are the flattened and disk-like rhizome, sulcate and reddish stem, chartaceous leaves with entire margin and umbellate staminate inflorescences.

Elatostema saxatile Triyutth. & L.F.Fu, sp. nov.

Figs 5, 6

Diagnosis

Elatostema saxatile is similar to E. bulbiferum Kurz, but differs by its flattened and disk-like rhizome, receptacle of pistillate inflorescences glabrous, staminode in pistillate flower 5, acute leaf apex and its sandstone habitat (Table 1).

Type

Thailand. Nakhon Phanom: Tad Kham Waterfall, 17°57.228'N, 104°9.6'E, 160 m alt., 13 September 2017, Triyutth. 200 (holotype KKU!; isotypes AAU!, BKF!, IBK!).

Description

Perennial herbs, lithophytic, monoecious, rhizomatous. Rhizome flattened, disk-like, 2–7 cm in diam., brownish. Stems 5–35 cm tall, simple or branched, succulent, greenish, glabrous. Stipules 2, persistent or sometimes caducous in reproductive stage, linear or lanceolate, membranous, glabrous. Nanophylls lanceolate to oblanceolate, 0.5–1.5 × 0.2–1.0 cm, chartaceous, glabrous, cystoliths fusiform. Leaves distichous, alternate; petiole 1–3 mm long, glabrous or puberulous; lamina asymmetrically elliptic to obovate, 1.5–7.0 × 0.5–3.0 cm, base oblique, margin serrate, apex acute, chartaceous; venation pinnate, major basal lateral veins absent, lateral veins 5–7 pairs; upper surface green, glabrous, cystolith fusiform, 0.2–0.5 mm long; lower surface greenish or cinereous, glabrous, cystolith fusiform, 0.2–0.5 mm long. Staminate inflorescences axillary, solitary, umbellate; peduncle 1–5 cm long, glabrous; receptacle absent; bracts lanceolate, 0.6–1.0 × 0.3–0.4 mm, membranous, pubescent; bracteoles lanceolate, 0.5–0.8 × 0.2–0.3 mm, membranous, pubescent. Staminate flowers 10–30 per inflorescence; pedicel 1.0–1.5 mm long, glabrous; tepals 5, ovate to oblong, 1.0–1.5 × 1.0–1.5 mm, apex obtuse, membranous, glabrous; stamens 5, filaments 1.0–1.5 mm long, anthers 0.6–1.0 mm long. Pistillate inflorescences axillary, solitary, capitate, 2–8 mm in diam., subsessile to pedunculate; peduncle 0.5–5.0 mm long, glabrous; receptacle elliptic, 2–4 mm in diam., membranous, glabrous; bracts lanceolate, 0.2–0.3 × 0.8–1.0 mm, membranous, pubescent; bracteoles lanceolate, 0.2–0.3 × 0.5–0.8 mm, membranous, pubescent. Pistillate flowers 20–50 per inflorescence; pedicel 0.5–1.5 mm long, glabrous; tepals 5, lanceolate, 0.8–1.2 × 0.2–0.4 mm, membranous, pubescent; staminodes 5, oblong, 0.1–0.2 × 0.1–0.2 mm; ovary superior, ovoid, 0.4–0.8 mm long. Achenes ellipsoid, 0.8–1.2 mm long, brownish, smooth.

Figure 5. 

Elatostema saxatile Triyutth. & L.F.Fu, sp. nov. A habit and habitat B leaf C staminate inflorescence D staminate flower E pistillate inflorescence F pistillate flower G achene (Drawn by N. Triyutthachai).

Figure 6. 

Elatostema saxatile Triyutth. & L.F.Fu, sp. nov. A habit and habitat B stem and rhizome C pistillate inflorescences D staminate inflorescence (Photos by Triyutth).

Distribution

Northeastern Thailand.

Ecology

Occurs on seasonal moist sandstone rocks in dry evergreen forest, at 100–200 m alt.

Phenology

Flowering and fruiting in May–October.

Etymology

The specific epithet refers to the habitat of this plant that dwelling on the rock.

Conservation status

This species was found scattered in ca. 6 locations in the Northeastern part of Thailand and the number of mature individuals is fewer than 1,000. According to IUCN (2022), E. saxatile should be assessed as Vulnerable (VN) according to criteria B2a and D1.

Additional specimens examined

Thailand. Buengkan: Chet Si Waterfall, 14 September 2017, Triyutth. 202 (KKU!), ibid., 27 April 2018, Triyutth. 266 (KKU!), 267 (KKU!), Chanean Waterfall, 14 September 2017, Triyutth. 203 (KKU!), Phu Wua, 21 May 2004, R. Pooma et al. 4201 (BKF!), 4202 (BKF!), 4191 (BKF!), ibid., 28 December 2011, M. Norsaengsri & N. Tathana 8707 (QBG!), ibid., 13 July 2016, Triyutth. 97 (KKU!), 98 (KKU!), Phu Sing, 26 August 2001, R. Pooma et al. 2694 (BKF!), Phu Tok, 27 April 2018, Triyutth. 268 (KKU!), Phu Tok Noi, 22 June 1995, C. Niyomdham 4448 (BKF!), ibid., 21 June 1997, C. Niyomdham 5052 (BKF!), Wat Tham Phra, Phu Wua, 20 May 2014, S. Sirimongkol et al. 593 (BKF!); Nakhon Phanom: Tad Kham Waterfall, 25 August 2001, R. Pooma et al. 2652 (BKF!), ibid., 13 September 2017, Triyutth. 199 (KKU!).

Notes

Elatostema saxatile was found growing on the sandstone rocks in Buengkan and Nakhon Phanom Provinces, in the Northeastern part of Thailand. This species is similar to E. bulbiferum in the presence of rhizome, presence of nanophyll and umbellate staminate inflorescences, but differed by its flattened and disc-like rhizome (vs rounded rhizome in E. bulbiferum), receptacle of pistillate inflorescences glabrous (vs pubescent), staminode in pistillate flower 5 (vs absent), acute leaf apex (vs acuminate to caudate apex). Moreover, E. saxatile was found on sandstone while E. bulbiferum was found on limestone substrates.

Acknowledgements

We are grateful to the Directors, Curators and staff of AAU, BCU, BK, BKF, C, HNU, IBK, K, KKU, L, P, PSU, QBG and SING for making the materials available for this study. This work was supported by the Applied Taxonomic Research Center, Khon Kaen University grant ATRC_R6102 and the Research Fund for Supporting Lecturer to Admit High Potential Student to Study and Research on His Expert Program Year 2016 from Graduate School and Faculty of Science, Khon Kaen University, the Carlsberg Foundation for the Flora of Thailand project, the National Natural Science Foundation of China (31860042) and the Light of West China Program of the Chinese Academic of Sciences ([2020]82).

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