Elatostema saxatile Triyutth. & L.F.Fu, 2022

Triyutthachai, Natthawut, Fu, Long-Fei, Triboun, Pramote, Wei, Yi-Gang & Pornpongrungrueng, Pimwadee, 2022, Three new species of Elatostema (Urticaceae) from Thailand, PhytoKeys 215, pp. 37-50 : 37

3. 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.

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.

Figures

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).