Elatostema rubricaule 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

2. 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.

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.

Figures

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).