Latin selago, an ancient name for some species of Lycopodium, +-ella, a diminutive suffix.

Plants small, terrestrial, epipetric or, rarely, epiphytic. Rhizomes prostrate, decumbent or erect, creeping, slender, leafy, producing roots (rhizophores) at bases or intermittently on creeping rhizomes. Stems prostrate or erect, branching repeatedly. Sterile leaves (trophophylls), bearing ligules, all alike, arranged spirally, small, simple, circular to linear, with single vein, or of 2 kinds and arranged in 4 ranks (2 lateral and spreading, 2 medial, appressed and ascending). Strobili on terminal branches and tips, composed of fertile leaves (sporophylls) different from sterile leaves. Sporangia of 2 kinds, borne at adaxial bases of sporophylls; microspores (20-60 µm diam.) and megaspores (200-600 µm diam.) borne in separate sporangia but on same strobilus.

Selaginellaceae (sometimes divided into five subgenera) contains the single genus Selaginella.