Polystichum paraobliquum 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 : 213-214

Polystichum paraobliquum Li Bing Zhang, M.Q.Han & Yan Liu , sp. nov. ( Figures 9 , 10 )

Type:— CHINA. Yunnan: Zhenxiong County, Chishuiyuan Town, Muguayuan Village, inside a limestone cave, elev. 1610 m, 27°31 ′ 50 ″ N, 104°53 ′ 16 ″ E, 29 May 2015, Mengqi Han & Jinquan Huang HMQ542 (holotype IBK!, isotypes CDBI!, MO!).

Diagnosis:— Polystichum paraobliquum is most similar to P. obliquum (D. Don 1825: 3) T. Moore (1858: 87) in having thick-papery and reflexed pinnae and obtuse pinna margins, but the former has smaller habit (shorter than 15 cm) and the lowest 2–3 pairs of pinnae are often sterile, while the latter has much larger habit (up to 40 cm) and all pinnae are often fertile.

Plants perennial, evergreen, 9–17 cm tall. Rhizomes ascending, ca. 2 cm long, ca. 1.5 cm diam., with remnant bases of old stipes; roots dark brown when dried, 1.5–5 cm long, ca. 0.1 mm diam. Leaves in tufts, 10–28 per rhizome; petioles 1.2–4 cm long, ca. 0.7 mm diam., basal portions densely covered with scales, scales ovate to ovate-lanceolate, 2–3.5 × 0.6–1 mm, chartaceous, brown, margins with lighter color and ciliate, apex long-caudate; distal petiole scales similar but narrower and shorter, ovate-lanceolate to lanceolate, 1–2.7 × 0.5–0.8 mm, membranous, margins ciliate, apex long-caudate. Laminae oblanceolate, 1-pinnate, 4–12 × 1.3–2.3 cm, apex acuminate, dark green; rachises ca. 0.6 mm diam., adaxially sulcate, scales similar to distal petiole scales but smaller, subulate or ovate-lanceolate, brown, 1–1.7 mm long including tip, 0.3–0.7 mm wide at base, margins regularly ciliate, apex long-caudate. Pinnae 6–15 pairs, oblong, 1–1.2 × 0.4–0.5 cm, basalmost 2–4 pairs gradually smaller toward lamina base, basalmost pair nearly 2/3 as large as middle ones, 0.1–0.5 cm apart, middle pairs 0.2–0.4 cm apart, all pinnae subcoriaceous, alternate, basiscopic margins entire, acroscopic margins shallowly toothed, teeth rounded and acute, basiscopic margins forming a 50–85° angle with rachis, apex acute to acuminate, base cuneate and asymmetric with acroscopic sides being much broader, petioles ca. 0.4 mm long, abaxially sparsely with microscales, microscales subulate, light brown, 0.5–1.7 mm long, 0.3–0.7 mm wide at base, margins with irregular outgrowths; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lower 2–3 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, 1–4 on acroscopic side of fertile pinnae, 0–2 on distal basiscopic side of fertile pinnae, ca. 0.8–1.2 mm diam., closer to pinna margins than to midrib (centers of sori 0.3–1.2 mm from pinna margins, 1–2.5 mm from midrib), centers 1.3–2 mm apart from one another; indusia rounded, lacerate. Spores round in polar view and elliptic in equatorial view; perispore sculpture cristate and granulate.

Geographical distribution:— Polystichum paraobliquum is only known from northeastern Yunnan, Southwest China. It is likely endemic to that limestone cave.

Ecology:— Polystichum paraobliquum grows inside a limestone cave at an elevation of 1610 m with humid and shady conditions.

IUCN Red List category:—CR-Critically Endangered: Only one population with about 100 plants was seen in the field.

Etymology:—The species epithet is based on the Latin prefix, para-, similar, and the Latin adjective, obliquum , oblique, the epithet of P. obliquum , referring to the similarities between the two species.

Taxonomic notes:— Polystichum paraobliquum is also very similar to P. puteicola Li Bing Zhang. H.He & Q.Luo (2010: 128) in having dark green, subcoriaceous, and oblong pinnae with acute apex and rounded-toothed margins. However, P. paraobliquum has basalmost 2–4 pairs of pinnae gradually smaller toward lamina base and the basalmost 2–3 pairs of pinnae sterile. In contrast, P. puteicola has basalmost pairs of pinnae not smaller toward lamina base and all pinnae are fertile. Our preliminary molecular analysis shows that these two species are indeed most closely related to each other. The two species are distributed far away from each other with P. paraobliquum being in southeastern Yunnan and P. puteicola in northwestern Guizhou.

Additional Specimen Examined:— CHINA. Yunnan: Zhenxiong County, Chishuiyuan Town, Muguayuan Village, inside a limestone cave, elev. 1610 m, 27°31 ′ 50 ″ N, 104°53 ′ 16 ″ E, 29 May 2015, Mengqi Han & Jinquan Huang HMQ543 (IBK, CDBI).

Figures

FIGURE 9. Polystichum paraobliquum.—A. Inside view of the cave where the new species was discovered.—B. Habitat and plant.—C, D. Portions of abaxial laminae.—E. Lower portion of plant.—F. Portion of abaxial lamina showing sori.—G. Portions of stipes showing scales.—H. Equatorial view of spore under SEM.—I. Polar view of spore under SEM.

FIGURE 10. Polystichum paraobliquum.—A. Habit.—B. Portion of abaxial lamina.