Polystichum membranifolium Li Bing Zhang, M.Q.Han & Yan Liu, 2016

Han, Meng-Qi, Liu, Yan & Zhang, Li-Bing, 2016, Seven new species of Polystichum (subg. Haplopolystichum; Dryopteridaceae) from southern China, Phytotaxa 280 (3), pp. 201-221 : 208-209

Polystichum membranifolium Li Bing Zhang, M.Q.Han & Yan Liu , sp. nov. ( Figures 5 , 6 )

Type:— CHINA. Yunnan: Wenshan City, Gumu Town, Tianwei Village, inside a limestone cave, elev. 1530 m, 23°09 ′ 29 ″ N, 104°11 ′ 21 ″ E, 21 April 2015, Mengqi Han & Jinquan Huang HMQ148 (holotype IBK!, isotypes IBK!, CDBI!, MO!)

Diagnosis:— Polystichum membranifolium is most similar to P. dielsii Christ (1906: 238) in having oblong and often reflexed pinnae, but the former has membranous pinnae, spinulose pinna margins, and entire indusia, while the latter has papery pinnae, pinna margins without spinules, and toothed indusia.

Plants perennial, evergreen, 12–17 cm tall. Rhizomes ascending, 1–1.5 cm long, ca. 1.7 cm diam., with remnant bases of old stipes; roots dull brown when dried, 2–10 cm long, ca. 0.9 mm diam. Leaves in tufts, 8–12 per rhizome; petioles 3–5 cm long, ca. 1 mm diam., basal portions densely covered with scales, scales ovate to ovate-lanceolate, 1.7–2× 0.6–1 mm, chartaceous, brown, margins with lighter color and short outgrowths to nearly entire, apex caudate; distal petiole scales similar but narrower and shorter, ovate-lanceolate to lanceolate, 1–1.5 × 0.3–0.7 mm, membranous, margins short-ciliate, apex caudate. Laminae oblanceolate, 1-pinnate, 7–13 × 0.7–2.1 cm, apex acuminate, yellowish green when dried; rachises 0.5–0.6 mm diam., adaxially sulcate, scales of rachis similar to distal petiole scales but smaller, subulate to ovate-lanceolate, dull brown, 0.7–1.5 mm long including tip, 0.1–0.4 mm wide at base, margins regularly ciliate, apex long-caudate. Pinnae 20–26 pairs, oblong, 0.5–0.9 × 0.2–0.4 cm, basalmost 3–6 pairs slightly smaller toward lamina base, basalmost pair about 2/3 as large as middle ones, 0.3–0.5 cm apart, middle pairs 0.2–0.4 cm apart, all pinnae membranous, alternate, basiscopic proximal margins entire, acroscopic margins and basiscopic distal margins toothed, teeth rounded and with spinules 0.2–0.4 mm long, basiscopic margins forming a nearly right angle with rachis, apex rounded, base cuneate and asymmetric, acroscopic sides being much broader, petioles ca. 0.5 mm long, abaxially with sparse microscales, microscales subulate to lanceolate, light brown, 0.4–0.8 mm long, 0.1–0.2 mm wide at base, margins with irregular outgrowths; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lower 5–8 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, 1–5(–6) on acroscopic side of fertile pinnae, 0–1 on distal basiscopic side of fertile pinnae, ca. 0.5 mm diam., closer to pinna margins than to midrib (centers of sori 0.2–0.9 mm from pinna margins, 0.6–1.1 mm from midrib), centers 0.7–1 mm apart from one another; indusia rounded, ca. 0.6 mm diam., margins entire when young and falling when old. Spores round in polar view and elliptic in equatorial view; perispore sculpture cristate with numerous spinules.

Geographical distribution:— Polystichum membranifolium is only known from southeastern Yunnan, Southwest China. It might be endemic to that limestone cave where it was discovered.

Ecology:— Polystichum membranifolium grows inside a limestone cave at an elevation of 1530 m with humid and shady conditions.

IUCN Red List category:—CR-Critically Endangered: Only one population with about 200 plants was seen in the field.

Etymology:—The species epithet is based on the Latin prefix, membrani-, membranous, and the Latin noun, folium, leaf, referring to the membranous leaves of the species.

Taxonomic notes:— Polystichum membranifolium is similar to P. crassirachis (see above) in having toothed pinna margins, but the former has membranous pinnae, thinner rachises, and rounded pinna apices, while the latter has papery pinnae, thicker rachises, and acute pinna apices. The new species has the thinnest pinnae among the species in P. subg. Haplopolystichum.

Additional Specimen Examined:— CHINA. Yunnan: Wenshan City, Gumu Town, Tianwei Village, inside a limestone cave, elev. 1530 m, 23°09 ′ 29 ″ N, 104°11 ′ 21 ″ E, 21 April 2015, Mengqi Han & Jinquan Huang HMQ150 (IBK!).

Figures

FIGURE 5. Polystichum membranifolium.—A. Inside view of the cave where the new species was discovered.—B–D. Habitats and plants.—E, F. Portions of abaxial lamina.—G. Stipes.—H. Equatorial view of spore under SEM.

FIGURE 6. Polystichum membranifolium.—A. Habit.—B. Portion of abaxial lamina.