Pteris trifoliolata H.J. Wei, 2022

Wei, Hong-Jin & Liang, Yong-Yan, 2022, Pteris trifoliolata (Pteridaceae), a new brake fern species from karst area in Guangxi, China, Phytotaxa 567 (1), pp. 100-104 : 100-103

Pteris trifoliolata H.J. Wei , sp. nov. ( Figs. 1 & 2 ).

Type: — CHINA. Guangxi: Du’an County, Yong’an Town , 108°07’N, 24°17’E, under shaded places in mixed forest on limestone mountain, alt. 802 m, 11 Aug. 2018, She-Lang Jin & Yong-Yan Liang JSL6444 (holotype, CSH! [No.159999]; isotypes, CSH!, IBK!) .

Diagnosis: — Pteris trifoliolata resembles P. nanlingensis but differs by its frond trifoliate (vs. with 1–3 pairs of lateral pinnae), sterile pinnae usually more than 3.5 (vs. less than 3.5) cm wide, fertile pinnae less than 5 (vs. more than 8) mm wide, and sorus acrostichoid (vs. marginal).

Description: Plant 63–80 cm tall. Rhizome short creeping, ca. 5 mm in diam., with scales at apex; scales ca. 2.5 mm long, narrowly lanceolate, black, with brown narrow edges, glossy, entire. Frond dense, dimorphic. Sterile fronds thinly leathery, adaxially green-brown, abaxially gray-green, glabrous on both surfaces; stipe 21–40 mm long, ca. 1.5 mm in diam, near middle, stramineous, base with sparse scales same as on rhizome, glabrous above base, grooved adaxially; lamina trifoliate, base rounded (sometimes shallowly cordate), 15–25 × (8.5–) 15–20 cm; apical pinna oblong to oblong-lanceolate, 13–22 × (3.5–) 4.5–5.7 cm, broadest at middle, apex subacute, attenuate into a tip 15–30 mm long, base cuneate or rounded cuneate, symmetrical, slightly decurrent, entire, stalked, stalk 5–25 mm, together with lower part of midrib shallowly grooved adaxially, pinna margins cartilaginous, undulate, serrate; lateral pinnae similar to apical pinna but smaller, 9.6–21.5 × (2.8–) 3.6–5 cm, ascending to obliquely spreading, falcate, often broader on basiscopic side, base asymmetrical, acroscopically cuneate to narrowly cuneate, basiscopically rounded cuneate, stalk 2–8 mm; veins free, simple or forked, ascending, parallel, ca. 8 per cm, vein tips enlarged, not reaching cartilaginous margin, faintly visible adaxially, obvious abaxially. Fertile fronds herbaceous or thinly papery; stipe 50–67 cm, 1.7 mm in diam. near middle, stramineous at base, upward castaneous–brown, grooved adaxially; Lamina trifoliate, 9.8– 14 × 4–7 cm, apical pinna linear, 8.4–13 cm long, 2–3 mm wide when immature, 3.5–4.5 mm wide when mature, base rounded cuneate, stalked, stalk stramineous, 5–12 mm, together with midrib shallowly grooved adaxially, apex mucronate, margins entire, midrib stramineous; lateral pinnae same as apical pinna but shorter, stalk 2–4 mm; veins sparse, invisible, apically enlarged and thickened to form oblong-shaped hydathodes, ca. 16 veins per cm, with a marginal black-brown veins connected to each other. Indusium linear, membranous, entire, reaching midrib, reflexed or rolling back at maturity. Sori acrostichoid.

Geographical distribution:— Pteris trifoliolata is only found in Du’an County, Guangxi, south China ( Fig. 3 ).

Ecology:— Pteris trifoliolata was discovered growing on a steep forested slope of a limestone mountain, at an elevation of about 800 m.

IUCN Red List category:— One small population with ca.15 individuals was found within an area of approximately 30 m 2 at a single locality situated in an unprotected karst area. The status of new species is currently considered as Critically Endangered (CR C2a(i); D) based on IUCN guidelines (IUCN 2019). This population is easily disturbed by human activities from nearby villages and is threatened with extinction at any time. For further assessments, more detailed investigations are needed to confirm if other populations and more individuals exist in similar habitats in karst regions.

Etymology:— The species epithet is based on the Latin trifoliolata , meaning three-leaved, referring to the trifoliate frond of the new species.

Chinese name:—三ŢÑAEẫ (san yu feng wei jue)

Additional specimens examined (paratype):— The same place as the holotype, 17 Jun. 2018, Yong-Hua Qin JSL6440A (CSH!).

Figures

FIGURE 1. Pteris trifoliolata.—A. Habitat.—B. Habit (individual plant).—C. Adaxial view of fertile lamina.—D. Sterile lamina.—E. Abaxial view of fertile lamina.—F. Rhizome and stipes.—G. Abaxial view of fertile pinna.—H. Adaxial view of fertile pinna.

FIGURE 2. Pteris trifoliolata.—A. Habit.—B. Portion of sterile pinna.—C. Portion of fertile pinna.

FIGURE 3. Geographical distribution of Pteris trifoliolata H.J. Wei in Guangxi Zhuang Autonomous Region, China.