A new species and a new series of Elatostema (Urticaceae) from south-western China

Abstract The new series ElatostemasectionWeddellia series Xingyiensia L.D. Duan & D.H. Yin (Urticaceae) is described. In addition, its new species Elatostemaxingyiense L.D. Duan & D.H. Yin, endemic to Guizhou Province, is also described and illustrated with photographs. The new series is morphologically similar to series Melanocarpa W.T. Wang and series Sublinearia W.T. Wang. The new species is most similar to E.melanocarpum, E.sublineare, E.obscurinerve, E.langicuspe and E.youyangense in morphology, but can be visibly distinguished by a combination of characters, including leaf vein, male inflorescences, female inflorescences and persistent tepals.


Introduction
The genus Elatostema J. R. Forster & G. Forster (1775: 53;Urticaceae) is part of the family Urticaceae and includes about 500 species of sub-shrubs and understorey herbs that grow in the deep shade of forests, gorges, stream sides and caves (Wang 2014;L.F. Fu et al. 2019a). More than 290 species occur in China (Wu et al. 2012) and the greatest species richness occurs on limestone karst in Southeast Asia (Lin et al. 2003;Wang 2014;L.F. Fu et al. 2019b). Elatostema is distinguished and characterised from other genera of Urticaceae by its inflorescences of determinate capitula with receptacles and involucres (Z.R. Yang et al. 2011).
We found an unknown species from Guizhou Province, south-western China during our field trips in February 2019 and March 2019. This species is morphologically most similar to Elatostema melanocarpum W. T. Wang, Elatostema sublineare W. T. Wang, Elatostema obscurinerve W. T. Wang, Elatostema langicuspe W. T. Wang and Elatostema youyangense W. T. Wang (Wang 1980(Wang , 1984(Wang , 2013. It differs distinctly from these known species in several morphological features (Table 1) and is described here as a new species.
The genus Elatostema includes four sections, sect. Pellionioides, sect. Weddellia, sect. Elatostema and sect. Androsyce. Based on the designations of sections and series by Wang (2014), the new species is a member of section Weddellia by having minute staminate receptacles. With the presence of a perennial herbaceous habit and penninerved leaves, the new species has traits consistent with ser. Crenata, ser. Nigrialata, ser. Nigribracteata, ser. Sublinearia, ser. Melanocarpa, ser. Stewardiana, ser. Bamaensia and ser. Involucrata. However, the male inflorescences are dichotomously branched, inconsistent with any series listed above. Therefore, a new series is described here.

Materials and methods
The species specimen was contrasted with the collections at IBK, PE and KUN. A morphological species concept that was developed as part of previous taxonomic research (Wei et al. 2011) was used. All morphological measurements were performed on dried and fresh specimens. Relevant literature was consulted for the identification of specimens (Wang 1980(Wang , 1984(Wang , 2013. The morphological characteristics of Elatostema xingyiense were determined using a stereomicroscope (Olympus SZX16) integrated camera system (Olympus DP27) and we made the specimen measurements by Olympus cellSens Entry. Relationship. The staminate capitula of the species is long peduncelate, as such this new series is closely related to ser. Sublinearia W.T. Wang (Wang 1980). It also has similarity to ser. Melanocarpa W.T. Wang with its achene fawn, ovoid, longitudinally 4(-5)-ribbed and tuberculate (Wang 2013). However, the new series differs from these two series with regards to the following features: leaf mid-vein impressed, the margin revolute (compared to the mid-vein flat and margin flat in ser. Melanocarpa and ser. Sublinearia); pistillate inflorescence peduncle dichotomously branched (compared to the peduncle not dichotomously branched in ser. Melanocarpa and ser. Sublinearia) ( Table 1). Relationship. This new species is closely related and similar to Elatostema melanocarpum (Wang 2013), Elatostema sublineare (Wang 1980), Elatostema obscurinerve (Wang 1980), Elatostema langicuspe (Wang 2013) and Elatostema youyangense (Wang 1984). This new species is visibly distinguished by a combination of characters: leaf mid-vein impressed, leaf margin revolute (mid-vein flat, margin flat in the other five species); pistillate inflorescence peduncle dichotomously branched (not branched in the other five species) (Table 1).
Etymology. The new species was named after its type locality, Xingyi City, Guizhou Province, China. Vernacular name. 兴义楼梯草(Xīng yì lóu tī cǎo) is Chinese Pinyin for Elatostema xingyiense, the first two characters are the place name of Xingyi City, the last three characters are the Chinese name for Elatostema.

Conservation status.
Elatostema xingyiense is only known from one collection with about 1000 individuals in Maling River Canyon Scenic Area, Xingyi City, Guizhou Province, south-western China (ca. 74 km 2 ). This species is under threat because of its fragmented habitat and there is tourism in the type location, Maling River Canyon Scenic Area. It is only in one small area of less than 100 km 2 and has threats from anthropogenic factors. We suggest that E. xingyiense should be considered as "Endangered" (EN) according to the IUCN Red List Categories and Criteria (IUCN 2019).