Polystichum napoense C.Xiong & R.H.Jiang, 2023

Xiong, Chi, Li, Zheng-Long, Yang, Zi-Meng, Jiang, Ri-Hong & Huang, Ting, 2023, Polystichum napoense (Dryopteridaceae), a new cave-dwelling fern species from Guangxi, China, Phytotaxa 601 (1), pp. 42-50 : 43

Polystichum napoense C.Xiong & R.H.Jiang sp. nov. ( Figs 1 & 2 )

Type: — CHINA. Guangxi Zhuangzu Autonomous Region: Baise City , Napo County, Longhe Town , Yuantuo village , 23.3897°N, 105.9864°E, elev. ca. 1080 m, 18 October 2022, Chi Xiong & Zheng-long Li DXGJ20221018-06 (holotype IBK!)

Diagnosis: — Polystichum napoense is characterized by its rhomboidal or deltoidovate pinnae, deflexed basal pinnae, and a large number of scales present on both surfaces of the pinnae.

Description:—Plants perennial, evergreen, 12–26 cm tall. Rhizome erect, short, ca. 2.5 cm in diam., covered with scales; scales broad ovate-lanceolate, brown, c. 3–4× 1–1.5 mm, margin erose, apex caudate. Fronds cespitose, 6– 15 per rhizome, 12–28 cm long; stipes green, 1.5–3.5 cm long, 0.4–0.6 mm in diam., stramineous, adaxially shallowly canaliculate; densely scaly; scales on base of stipe long-triangular to lanceolate, membranous, dark brown, 1.5–3 × 0.5–1 mm, margin sparsely toothed, apex acuminate to caudate; scales on distal petiole similar but narrower. Lamina lanceolate, 9–25 × 2–2.5 cm, base slightly contracted, apex acuminate, 1-pinnate; rachis stramineous, covered with scales; scales lanceolate, narrowly lanceolate to sublinear, membranous, dark brown, 0.5–1.5 × 0.1–0.3 mm, with 1–3 teeth on margin, apex fibriform. Pinnae 10–25 pairs, chartaceous, greyish green, alternate, slightly imbricate, subexplanate, attached at 80–150° to rachis, short petiolate, rhomboidal or deltoidovate, 0.8–1.8 × 0.5–0.7 cm at middle, base asymmetric, acroscopic base auriculate, margin repand, basiscopic base truncate and forming a 15–40(–60)° angle with rachis, margin dentate, apex obtuse, both surfaces scaly; scales linear, filiform, ca. 0.5 mm long; veins pinnate, abaxially slightly distinct, adaxially indistinct. Sori terminal on veins of distal pinnae, close to pinna margin, 8–13 (3–5 below midrib, 5–8 above midrib) per fertile pinna; indusia absent. Sporangia almost round, 0.3–0.4 mm diam., ca. 0.1 mm thick, dark brown when mature; annuli with 15–17 thickened cells. Spores circular in the polar view and elliptic in the equatorial view, 43.8–47.5 (–50.3) × 50.8–59.4 (–63.8) µm (polar axis × equatorial axis); the ratio of the length of the polar axis to that of the equatorial axis is 0.74–0.87; perispore sculpturing is alveolate or forming large folds on it.

Distribution and ecology: — Polystichum napoense is currently found only from the type locality at an elevation of ca. 1080 m. This species grows on rocks in a karst cave, spanning from the entrance zone to the twilight zone.

Etymology: —Derived from the type locality, Napo County (Guangxi, China).

Vernacular name:—Ďāff̎ (nà pô ěr jué).

Conservation status: — Polystichum napoense is currently known only to exist in one population at the type locality. The population size is estimated to be around 100–150 mature individuals. Following the IUCN ( The International Union for Conservation of Nature and Natural Resources) guidelines ( IUCN, 2023), the species is temporarily assessed as Critically Endangered (CR).

Figures

FIGURE 1. Polystichum napoense.—A. Habit.—B. Basal pinna.—C. Upper pinnae.—D. Petiole scales.—E. Rachis scales. (Drawn by Yi-Chen Wang based on the holotype).

FIGURE 2. Polystichum napoense.—A. Habitat.—B, C. Plants in the field.—D. Adaxial view of the frond.—E. Abaxial view of the frond.—F.A portion of rachis with a portion of pinnae (adaxial view).—G.A portion of rachis with a portion of pinnae (abaxial view).—H. A portion of the abaxial lamina.—I. Scales from stipes (a–c), rachis (d–f).—J. SEM micrographs of spores. (A photographed by Jia-xin Fu, J by Yu-Jing Wei, and others by Chi Xiong)