22. Asplenium ceterach Linnaeus, Sp. Pl. 2: 1080. 1753.
药蕨 yao jue
Ceterach officinarum Willdenow; Hemidictyum ceterach Beddome.
Plants up to 12 cm tall. Rhizome erect, short; scales dark brown in center to pale brown at margin, ovate-triangular, margin sparsely toothed. Fronds caespitose; stipe brown, short, 2-4 cm; lamina narrowly elliptic, 5-8 × 1-1.6 cm, reduced to base, pinnatipartite, apex obtuse; segments 6-8 pairs, alternate, triangular, bases adnate to rachis, entire or slightly sinuate, apex obtuse. Veins obscure, nothocatadromous (anadromous base pattern but several middle pinnae with their basal vein pair catadromous), anastomosing and forming subhexagonal submarginal areoles. Fronds subleathery, dark green to brownish green after drying, adaxially subglabrous, abaxially densely covered with brownish, ovate-lanceolate to ovate scales, average stomatal guard cell length 40-48 µm. Sori linear, usually on acroscopic secondary veinlets and in middle between costa and margin; indusia rudimentary. Spores with lophate (costate) perispore, average exospore length 37-42 µm. Plants sexual tetraploid: 2n = 144.
In dry rock crevices; 1400-2600 m. Xinjiang, N Xizang [Afghanistan, N India, Kashmir, Pakistan; N Africa, SW Asia, Europe].
Asplenium ceterach is widely distributed in S Europe and was often put into the separate genus Ceterach Willdenow (Anleit. Selbststud. Bot. 578. 1804, nom. cons.; 药蕨属 yao jue shu) on the basis of its peculiar pinnatipartite fronds, submarginally anastomosing veins, and the dense, abaxial scale covering. However, all these characters also occur in other clades within the family, and molecular studies (Van den heede et al., Amer. J. Bot. 90: 481-495. 2003) have shown that "Ceterach" consists of two separate clades both nested within Aspleniaceae and not meriting generic status. This species is autotetraploid; its diploid ancestor (A. javorkeanum Vida), from which it can be distinguished by its larger spores, is only known from the Mediterranean area.