苍山蕨 cang shan jue

Asplenium alternans Wallich ex Hooker; Ceterach alternans Kuhn; C. dalhousiae (Hooker) C. Christensen; Ceterachopsis dalhousiae (Hooker) Ching.

Plants 13-15(-25) cm tall. Rhizome erect, short; scales brown to dark brown, narrowly triangular to lanceolate, margin with short teeth. Fronds caespitose; stipe short, less than 2 cm; lamina narrowly elliptical-obovate, 4-15 × 1.8-5 cm, gradually narrowed at base, pinnatipartite, apex acute to obtuse; segments 10-14 pairs, alternate, ovate to narrowly ovate, 8-12 × 5-8 mm, margin entire and hyaline, apex obtuse. Veins obscure, nothocatadromous (anadromous base pattern but several middle pinnae with their basal vein pair catadromous), lateral veins 6-8 pairs, often forking near margin. Fronds firmly papery, brownish yellow to dark brownish green when dry, glabrous, average guard cell length 45-54 µm. Sori 5-7 pairs per segment, 3-5 mm, oblique, on acroscopic secondary veinlets; indusia pale brown, linear, membranous, mostly opening toward costa. Spores pale brown, average exospore length 26-30 µm, outer perispore folded (lophate) and with small pores. Plants sexual diploid: 2n = 72.

On rocks; 1000-3000 m. ?Xizang [Afghanistan, India, Kashmir, Nepal, Pakistan; isolated populations in Africa, North America (Mexico, United States)].

Asplenium dalhousiae is a relatively common W Himalayan fern expected to occur in Xizang as it has been reported for Nepal (Roy et al., Brit. Fern Gaz. 10: 194. 1971); it is recorded provisionally in the Flora. This and the following three taxa (A. paucivenosum, A. magnificum, A. qiujiangense) were often included in the genus Ceterachopsis (J. Smith) Ching (Bull. Fan Mem. Inst. Biol., Bot. 10: 8. 1940; 苍山蕨 属 cang shan jue shu) on the basis of their peculiar frond morphology. The group consists of four or five species, mainly from the subtropical mountains of SW China, and one (A. dalhousiae) more widely distributed taxon. Recent studies have confirmed that this clade does not merit generic rank.