Scientific name: Leptochilus oblongus Li Bing Zhang, Liang Zhang & Ngan T.Lu
English name:
Vietnamese name: Ráng môi mỏng thuôn
Other name:

Type:

VIETNAM. Hoa Binh Province: Lac Son District, Ngoc Son Ngo Luong Nature Reserve, elev. 640–700 m, 20°25’N/105°20’e, on limestone rocks in disturbed rainforest, 20 November 2013, L.-B. Zhang, L. Zhang & N. T. Lu 6299 (holotype VNMN!; isotypes CDBI!, MO!).

Description

Plants perennial, evergreen. Rhizome creeping, ca. 1.2-1.5 mm in diam., dorsiventrally flattened, densely scaled, with few short roots; cross section of rhizome with 7-10 vascular bundles, irregularly shaped, scattered sclerenchyma strands 25-30; scales peltate, dark brown and more or less shining, clathrate, membranous, margins entire or sparely denticulate, polymorphism: the ones appressed on the rhizome often ovate or elliptic, 0.5-0.7 × 0.4-0.6 mm, the spreading scales lanceolate with twisted apex, 1.0-1.3 × 0.8-1.0 mm. Fronds nearly dimorphic, 0.5 to 3.0 cm distant, (16-)25-30 cm long; stipe stramineous, (9-)14-17 cm long, ca. 0.5-1.0 mm in diam. at middle, slightly winged at distal part, less than 1.5 mm wide, with spare scales at base; rachis narrowly winged, 4.0-4.5 mm wide at the distal part, 2.8-3.5 mm at base. Lamina oblong-ovate or ovate-lanceolate, deeply 1-pinnatifid, (8-)10-13 × 7-9 cm, widest below middle of lamina, thinly papery, dark brown when dry, glabrous, margins of lobes entire and distinctly undulate. Lobes (3-)5-7 pairs, narrowly lanceolate, apex acuminate, 4-6 × 0.4-0.9 cm, basal portions of lobes obviously narrowed, ca. 1/2 to 2/3 as wide as middle portions, slightly ascending upward, basiscopic margins of lobes at angles of 45-80 degree with rachis, distal pairs of lobes slightly narrowed, ca. 3/4 to 4/5 as long as middle ones, opposite or slightly alternate, middle pairs of lobes close to each other, basal pairs of lobes distant with each other in 0.9-1.2 cm. Midribs slightly raised, lateral veins invisible. Sori oblong, (3-)6-12(-15) on each side of lobe, 0.8-1.2 × 1.0-1.5 mm, close to lobe margins (centers of sori 0.5-1.1 mm from lobe margins, 1.6-3.5 mm from midrib), centers ca. 3.8-5.3 mm apart from one another. Sporangia round, ca. 0.2 mm in diam., dark brown and often separated from stalks when mature, stalks ca. 0.3 mm long. Spores irregularly in shapes, green to pale green, 32 per sporangium. Paraphyses absent.

Geographical distribution

Currently, Leptochilus oblongus is only found in Lac Son District, Hoa Binh Province and may represent a species endemic to Vietnam. Ecology:—Leptochilus oblongus was observed to grow in the crevices among limestone rocks in a slightly disturbed rainforests, at elevations between 640 and 700 m.

IUCN Red List category

Only one population with about 10 individuals of L. oblongus were found. The status of the new species can be classified as Critically endangered (CR), based on current information and following the IUCN (The International Union for Conservation of Nature and Natural Resources) guidelines (IUCN, 2011), but more extensive fieldwork in surrounding similar habitats is needed to accurately assess its conservation status. The preservation of the rain forests in Vietnam is the key to conserve this species. Fortunately, the species was discovered in the Ngoc Son Ngo Luong Nature Reserve and all the natural habitats of the nature reserve are protected.

Etymology:

The epithet oblongus refers to the oblong sori which are rare in the genus.