Description from Flora of China
Plants herbaceous, terrestrial, epilithic, or occasionally epiphytic, evergreen or sometimes seasonally green, perennial (rarely annual). Rhizome erect, prostrate, creeping, ascending, or scandent, branched. Rootlike rhizophores borne on dorsal (upper) or ventral (lower) side in axils of branches, confined to lower part of rhizome or throughout, simple or branched. Roots formed at tip of rhizophore, branched. Leaves simple, 1-veined (exceptionally forked), each bearing a ligule in axil on adaxial surface, monomorphic or dimorphic, spirally arranged or in most species arranged in 4 ranks, 2 ranks on dorsal or upper side of stem and branch (called median or dorsal leaves), other 2 ranks on lateral or lower side (called lateral or ventral leaves). Strobili at apex of main stem or branch or lateral to branchlet, compact or lax, tetragonal, complanate or rarely cylindrical; sporophylls arranged in 4 ranks, monomorphic or dimorphic; in dorsiventral strobili with dimorphic sporophylls, dorsal (upper) sporophylls of most species larger than ventral (lower) ones (=resupinate), dorsal sporophylls normally green and firm in texture, while ventral ones paler and somewhat membranous, or dorsal sporophylls smaller than ventral sporophylls (=non-resupinate); in some dorsiventral strobili, dorsal sporophylls bearing outgrowths on lower surface, like a flap, termed "sporophyll-pteryx," partially covering sporangium proximal to it. Sporophylls various, ranging from ovate to ovate-lanceolate, margin denticulate, ciliolate, or entire, apex acute and entire, with ligules distal to sporangia. Sporangia single per sporophyll, heterosporangiate (megasporangium and microsporangium). Spores heterosporous, megaspores ca. 10 × as large as microspores, megaspores 4, rarely 1 per sporangium, microspores more than 100; spores trilete, tetrahedral-globose, or nearly spheroidal, and often bearing equatorial flange. x = 8, 9, 10.
Zhang Xianchun. 2004. Selaginellaceae. In: Zhang Xianchun, ed., Fl. Reipubl. Popularis Sin. 6(3): 86-219.
One genus and ca. 700 species: almost cosmopolitan, with its highest diversity in the tropics; 72 species (23 endemic, one introduced) in China.
(Authors: Zhang Xianchun (张宪春); Hans P. Nooteboom, Masahiro Kato)