16. Selaginella sibirica (J. Milde) Hieronymus, Hedwigia. 39: 290. 1900.
Selaginella rupestris (Linnaeus) Spring forma sibirica J. Milde, Fil. Eur., 262. 1867
Plants on rock or terrestrial, forming discrete long-spreading mats or seldom cushionlike mats. Stems radially symmetric, creeping or decumbent, not readily fragmenting, irregularly forked, without budlike arrested branches, tips straight; main stem indeterminate, lateral branches conspicuously or inconspicuously determinate, often strongly ascending, 1--3-forked. Rhizophores borne on upperside of stems, throughout stem length, 0.2--0.37 mm diam. Leaves monomorphic, in alternate pseudowhorls of 5, tightly appressed, ascending, green, linear-lanceolate to narrowly lanceolate, 2--3.5 X 0.35--0.5 mm (smaller on lateral branches); abaxial ridges prominent; base cuneate and decurrent to rounded and adnate on young lateral branches or buds, glabrous or sometimes pubescent; margins long-ciliate, cilia transparent, spreading to ascending, 0.07--0.17 mm; apex keeled, truncate in profile, obtuse to attenuate; bristle white to whitish or transparent, puberulent, 0.45--0.8 mm. Strobili solitary, 0.5--2.5 cm; sporophylls deltate-ovate to ovate-lanceolate, abaxial ridges well defined, base glabrous, margins ciliate, apex truncate in profile, bristled. 2 n = 18.
Dry, alpine, rocky slopes, rock crevices, granite rock, limestone boulders, sandstone, bare open grassy tundra; 130--2400 m; N.W.T., Yukon; Alaska; Asia in Japan and the former Soviet republics.
Selaginella sibirica is most closely allied to S . rupestris . In addition to differences noted in the descriptions, it can be distinguished from S . rupestris by the numerous marginal cilia on the leaves and by the transparent sporophyll margins; S . rupestris has a variable number (usually few) of marginal cilia and nontransparent sporophyll margins.