Argostemma ehuangzhangense H.G.Ye, Jia Liu & W.B.Liao, 2022

Liu, Zhong-Chong, Liu, Jia, Zhao, Wan-Yi, Fan, Qiang, Ye, Hua-Gu, Wang, Lei & Liao, Wen-Bo, 2022, Argostemma ehuangzhangense (Rubiaceae), a new species from Guangdong, China, PhytoKeys 214, pp. 75-82 : 75

Argostemma ehuangzhangense H.G.Ye, Jia Liu & W.B.Liao sp. nov.

Type.

China. Guangdong Province: Yangchun City, Bajia Town, E’huangzhang Nature Reserve , near the Wufu Waterfall , 21°52'N, 111°25'E, a.s.l. 720 m, 3 May 2018, Wan-Yi Zhao, Jia Liu, Qiao-Ling Ding, Fan Ye YC-2018-02 (holotype: SYS!, Barcode SYS00236851; isotype: SYS!, Barcode SYS00236852) (Figs 1 , 2 ) .

Diagnosis.

Argostemma ehuangzhangense is similar to A. lamxayanum and A. laotica in its habit and pseudo-verticillate leaves, but differs in having terminal solitary 4-merous flowers, short anthers (1.2-1.5 mm long) opening by longitudinal slits.

Description.

Terrestrial perennial herbs, 1-4 cm tall, attached to the substrate by tubers flattened globose, with a few roots. Stems erect, densely pubescent, with one pair of scale-like leaves at the lower middle portion. Leaves four per individual, clustered at the stem apex, verticillate, anisophyllous, petiole 0.5-2 long mm; blades membranous or thinly papery when dried, ovate to elliptic, 5-25 × 3-12 mm, cuneate at base, acute to obtuse at apex, margins entire; adaxial surface green, densely antrorse strigose; abaxial surface grey-white with white particles, sparsely pubescent on the midrib vein and lateral veins; lateral veins 3- or 4-pairs; stipules deciduous. Flowers solitary, terminal; pedicels 0.8-1.8 cm, with densely pubescent, trichomes multicellular. Calyx densely pubescent, trichomes multicellular, hypanthium portion obovoid; lobes 4, subtriangular, 1-1.3 × 1.1-1.4 mm, abaxially pubescent, adaxially glabrous. Corolla white, rotate, external surface sparsely pubescent, internal surface glabrous, corolla tube 0.3-0.6 mm long; corolla lobes 4, oblong-lanceolate, 3-4 × 1.5-2 mm. Stamens 4; filaments free, 3.5-4 mm, exserted; anthers 1.2-1.5 mm long, coherent into a tube, dehiscent longitudinally. Ovary 2-locular, ovules numerous in each locule; style filiform, ca. 4 mm, with short pubescence, stigma capitate, exserted. Capsule obovoid, 2-5 mm in diameter, 1-3 mm long, pubescent, crowned by a persistent calyx, without ribs or furrows.

Phenology.

This species is recorded flowering in March-May and fruiting in May-September.

Distribution.

Argostemma ehuangzhangense is endemic to E’huangzhang Nature Reserve, southwestern Guangdong Province. It is currently known only from two populations recorded in county of Dianbai and city of Yangchun.

Habitat.

Growing along river on wet sandstone under the evergreen broad-leaf forest at 400-750 m a.s.l.

Etymology.

The specific epithet ‘ehuangzhangense’ is derived from the type locality, E’huangzhang Nature Reserve of the Guangdong Province, in China. This area is the oldest geological platform in the Guangdong Province, in which many endemic species occur ( Wang et al. 2003; 2004; Ding et al. 2018). The new species is also expected to occur in the Yunkaishan National Nature Reserve, Maoming City, because this area shares a similar tectonic history with E’huangzhang. Therefore, we proposed for the vernacular name of the species as yuèxīxuěhuā (粤西雪花).

Preliminary conservation status.

The species is endemic to the Guangdong Province. According to our field survey, there are only two localities in which Argostemma ehuangzhangense is recorded and each population consists of 100-250 individuals. The number of mature individuals of Argostemma ehuangzhangense is more than 400, but less than 1000. Thus, we believe that Argostemma ehuangzhangense would be considered VU (Vulnerable) in an official IUCN Red List assessment ( IUCN Standards and Petitions Subcommittee 2022) according to the D criterion.

Paratypes.

China. Guangdong Province: Yangchun City, Bajia Town, E’huangzhang Nature Reserve, 21°52'N, 111°25'E, a.s.l. 704 m, 29 Apr. 2017, Hua-Gu Ye, Zhong-Chong Liu YHG-06 (SYS); same locality, 5 Aug. 2017, Hua-Gu Ye, Wan-Yi Zhao, Zhong-Chong Liu YC2017-35 (SYS); Yangchun City, Bajia Town, 21°52'N, 111°25'E, a.s.l. 750 m, 1 Aug. 2001, Hua-Gu Ye 6119 (IBSC); Dianbai County, Luokeng Town, Shuangjifeng, 21°52'N, 111°21'E, a.s.l. 400 m, 8 Aug. 2001, Hua-Gu Ye 6427 (IBSC).

Figures

Figure 1. Argostemma ehuangzhangense A individuals in their natural habitat B flowering individuals C fruiting individuals D side view of an individuals with tuber E leaf blade adaxial surface view F leaf blade abaxial surface view G flower, internal corolla surface view H folwer, external corolla surface view I capsule, top view J stamen K style and stigma tightly enclosed by stamens L ovary longitudinal section view. (photographs (A-G) were taken by Wan-Yi Zhao in the original habitat area of E'huangzhang and photographs (H-L) were taken by Jia Liu in SYS Herbarium in May 2018).

Figure 2. Argostemma ehuangzhangense A flower B fruit C style and stigma D habit of a mature plant E multicellular trichomes present on the stem, pedicel and ovary F corolla G organization of stamens H stamen (Drawn from living plants by Yun-Xiao Liu).