Scientific name: Pteris langsonensis Li Bing Zhang, Liang Zhang & NEnglish name: Vietnamese name: Ráng seo gà lạng sơnOther name:
VIETNAM. Lang Son Province: Huu Lung District, Huu Lien Commune, 21°39'33.53"N/106°22'03.74"E, in the acidic soils in the evergreen forest, 200-220 m, 20 November 2013, L.-B. Zhang, L. Zhang & N. T Lu 6593 (holotype VNMN-2015.00100!, isotypes CDBI!, MO!, VNMN!).
Diagnosis: Pteris langsonensis is most similar to P. plumbea in having 1-pinnate leaves with basal pairs of pinnae lobed, but the former has typical dimorphic leaves and fertile pinnae much contracted and with a width of no more than half of sterile pinnae. It is also similar to some individuals of P. cretica Linnaeus (1767:130), but can be distinguished from the latter by having smaller habit and slightly tooted leaf margins.
Plants perennial, (25-)40-50 cm. Rhizomes ascending or shortly creeping, ca. 1.2-3.5 cm long, 2.8 mm in diam., with roots and persistent petiole bases; roots brown when dry, up to 5 cm long, 0.2 mm in diam., covered with fine curved short hairs; scaly on rhizomes where leaves arise, scales very rare on remaining parts of rhizomes, ca. 1.6 x 0.4 mm, bicolor, blackish brown and shiny at middle, light brown on margins, lanceolate, subentire, slightly curly towards apex. Leaves clustered, up to 12 leaves per rhizome, dimorphic, sterile leaves usually 3 to 5 times as fertile leaves on the same rhizomes. Sterile fronds 25.0-30.0 cm long; petiole 14.0-16.0 cm long, 0.3-0.5 mm in diam. in middle, base reddish brown, upwards green or pale brown, grooved adaxially, distal petiole slightly winged; lamina oblong or ovate-oblong in outline, 12.0-15.0 x 5.0-7.0 cm, papery in texture, green when fresh and grayish when dried, glabrous on both surfaces, pinnate. Pinnae 2-3 pairs, 2.1-4.2 cm distant with each other, linear-lanceolate, 4.1-6.2(-9.0) x 0.9-1.4 cm, sessile or basal most pair of pinnae 3.5-7.5 mm petiolate, cuneate and decurrent at base, blunt or caudate at apex, costae of lateral pinnae at angles of 60-85 degree with rachis; terminal pinnae the same size or longer than lateral pinnae, sometimes base lobed, decurrent to rachis; basalmost 1(- 2) pairs of pinnae lobed, lobes shortly linear-lanceolate, 2.5-3.1 x 0.7-1.1 cm; margins of pinnae and lobes entire at cuneate bases, slightly toothed upwards but conspicuously toothed at apex, teeth deltate with cartilaginous tips; costae and petiolules if present pale green, canaliculate adaxially, raised abaxially; the intersections of grooves of costae and rachis with 3 to 5 spine-like or squamiform outgrowths. Fertile fronds ca. two times longer than sterile fronds; petiole 18.8-24.3(-26.0) cm long, 0.4-0.6 mm in diam. in middle; lamina oblong in outline, 18.5-19.8 X 7.3-8.5 cm; pinnae 3-5, broad linear, 5.4-11.5 X 0.27-0.55 cm. Venations free, distinct abaxially and merely visible adaxially, simple or 1(-2)-times forked, almost reaching cartilaginous pinna margins, middle points of veins 0.5-0.8 mm (sterile leaves) or 0.8-1.1 mm (fertile leaves) distant with each other. Sori marginal on both sides of fertile pinna, 4.0-6.5 mm above the base and 5.5-9.0 mm below the apex, linear, 4.7-9.8 cm long, 0.5-0.8 mm wide; indusia membranous, margins subentire, light grey, 0.6-0.9 mm wide. Sporangia elliptic, ca. 0.25 X 0.29 mm, dark brown and often separated from stalks when mature, stalks ca. 0.45 mm long. Spores irregularly in shapes, pale yellow, 32 per sporangium.
Geographical distribution:—Pteris langsonensis is only known from Huu Lien Commune, Huu Lung District, Lan Ti Village, Lang Son Province, northern Vietnam. The two populations of the new species were observed to occur in a moderately disturbed evergreen forest by a large lake. It is possible that the new species occurs in the mountains with acidic soils developed from limestones in the adjacent provinces of Vietnam yet to be explored.
Ecology:—Pteris langsonensis was observed to grow in wet acidic soils in the rainforest, at elevations between 200 and 220 m. Both populations were by a lake and 2 to 3 m away from the water surface.
IUCN Red List category:—Only two large populations with about 50 individuals of Pteris langsonensis have been found. The status of the new species can be classified as Critically Endangered (CE), based on current information and following the IUCN (The International Union for Conservation of Nature and Natural Resources) guidelines (IUCN Standards and Petitions Subcommittee, 2014), but more extensive fieldwork in surrounding similar habitats is needed to accurately assess its conservation status. The habitat and its surrounding regions are located in the protected Huu Lien Nature Reserve, Lang Son Province.
Etymology:—The species epithet longsonensis is derived from the name of the province in northern Vietnam, Lang Son, where the plants were found.