Selaginella austro-orientalis H. J. Wei & X. M. Zhou 2023, sp. nov.

Selaginella austro-orientalis H.J. Wei & X.M. Zhou, sp. nov. (Figs. 1 & 2) Type:— CHINA. Jiangxi: Guixi City, Zhangping Town, Shuangzhen Village, in a valley, 117°22’43”E, 27°56’33”N, elev. 300 m, 8 June 2021, She-Lang Jin, Bin Chen, Si-Gang Li, et al. JSL8054 (holotype: CSH0195000!; isotypes: CSH!, IBK!, PE!, PYU!). Diagnosis:— Selaginella austro-orientalis is superficially similar to S. heterostachys, but differs by having ventral leaves spreading, broadly ovate in outline and short-cuspidate at apex, and megasporangia only present at ventral sporophylls. Description: Plants terrestrial or epilithic, seasonally green, decumbent or nearly ascending; fertile stems erect. Rhizophores confined to decumbent stem and lower portion of erect stem, born on ventral side in axils of branches, 2–7 cm long, slender, 0.15–0.20 mm in diam., root much forked. Main stem pinnately branched, straight or slightly zigzag, stramineous, 0.35–0.45 mm in diam. in lower part, terete, glabrous, with single vascular bundle, erect fertile stems 6–10 cm, 2–3 times pinnately branched, main stem including leaves 3–5.7 (–6.8) mm wide at middle; primary branches 3–4 pairs, adjacent primary branches 1–2 cm apart, once or twice pinnately branched, secondary branches once or twice forked, tertiary branches forked or simple, branchlets sparse and regular, ultimate branches including leaves 3.0– 4.5 mm wide. Leaves herbaceous. Axillary leaves symmetrical, those on branches smaller than those on main stem, base subcordate, margins minutely denticulate, ovate or oblong, 1.1–2.0 × 0.5–1.2 mm. Dorsal leaves asymmetrical, those on branches sparser than those on main stem, not approximate, ovate or ovate-lanceolate, 1–1.5 × 0.5–0.7 mm, not carinate, base rounded-cuneate or obliquely attenuate, exauriculate, margins minutely denticulate, apex acuminate or shortly aristate, sometimes reflexed. Ventral leaves asymmetrical, those on main stem obviously larger than those on branches; ventral leaves on branches distant or approximate, spreading, seldom deflexed, those on fertile branches ascending distally, broadly ovate or ovate, 1.8–3.5 × 1–2.4 mm, margin minutely denticulate, apex acute, obtusely cuspidate or slightly cuspidate; basiscopic base rounded; acroscopic base rounded-truncate, broader, not enlarged, not overlapping stem and branches, or overlapping fertile stem and branches more or less. Strobili solitary or binate, terminal, compact, dorsiventrally complanate, resupinate, 3.0–14.5 × 1.8–3.5 mm; sporophylls dimorphic; dorsal sporophylls ovate-lanceolate or oblong-lanceolate, falcate, not keeled, margin denticulate, apex acuminate or aristate, with sporophyll-pteryx complete and denticulate; ventral sporophylls ovate-lanceolate, carinate (ridge also denticulate), margin ciliolate-denticulate to denticulate, apex long acuminate; megasporophylls distributed in basal portion on lower side of strobilus, or throughout lower side, or megasporophylls and microsporophylls at intervals when strobili fully developed. Megaspores ivory-white or whitish, suborbicular in polar view, 200–230 μm in polar axis; prominent laesurae extend 3/4 of the distance to the equator, both proximal and distal surfaces densely covered with verrucae and tuberculate ornamentations of 2–5 μm wide, ornamentation surface with finely echinulate microsculptures. Microspores yellowish-orange, rounded-triangular to suborbicular in polar view, 31–34 μm in polar axis, prominent laesurae extend 3/4 of the distance to the equator; both proximal and distal surfaces covered with coarsely and shallowly papillate elements (Fig. 1. L, M, N). Distribution, habitat and ecology:— Selaginella austro-orientalis was found in Jiangxi, Zhejiang and Fujian Province respectively, and is endemic to southeastern China (Fig. 3). The new species occurs at elevations of ca. 10–625 m, and grows on rocks or soil banks in open forests or sunny slopes, especially in the valleys. Conservation assessments:— Selaginella austro-orientalis was only found at three sites in three provinces of China. The populations of each site spread at an area of ca. 50–110 km 2 respectively, with the total number of at least 5000 individuals in these three sites. The new species is very common in the localities but very rare outside these areas. Currently, the new species can be considered as NT (Near Threatened) according to the IUCN guidelines (IUCN 2022). Etymology:— The epithet of the new species reflects that it was collected in southeastern China. Chinese name: ṪDzṫffi (dong nan juan bai). Additional specimens examined (paratypes):— CHINA. Jiangxi Province, Guixi City, Lengshui Town, Raoyuan station, elev. 385 m, 29 Apr. 2021, She-Lang Jin & Bin Chen JSL7960 (CSH!), elev.. 260–600 m, 30 Apr. 2021, SheLang Jin, et al. JSL7965 (CSH!, IBK!, PE!, PYU!) and JSL7982 (CSH!); Zhejiang Province, Yueqing City, Dajing Town, Nanmen Village, elev. 36 m, 29 May 2022, Yu-Ting Zhang CFH09012417 (CSH!); Fujiang Province, Minhou County, Nanyu Town, alt. ca. 400 m, 19 May 2017, Xiang-Xiu Su CSH22791 (CSH!).Published as part of Wei, Hong-Jin, Chen, Bin, Fang, Shao-Li & Zhou, Xin-Mao, 2023, Selaginella austro-orientalis (Selaginellaceae), a new species from Southeast China, pp. 87-97 in Phytotaxa 579 (2) on page 91, DOI: 10.11646/phytotaxa.579.2.2, http://zenodo.org/record/754305