﻿Three new species of Elatostema (Urticaceae) from Thailand

﻿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. Elatostemakaweesakii is similar to E.atroviride. Elatostemakaweesakii 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. Elatostemarubricaule and E.saxatile are found on sandstone habitats. They have distinct flattened and disk-like rhizome. Elatostemarubricaule is distinguished by its distinct sulcate and reddish stem with flattened and disc-like rhizome and chartaceous leaves with entire margin. Elatostemasaxatile 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.


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 This suggests that the species diversity documentation in Thailand was out of date due to its under-sampled status (Middleton et al. 2019).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.
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.
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. 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).
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. Latin saxum, rock, and atile, place of growth, alluding to habitat of the new species among rocks 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)   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.