Equisetaceae A. P. DC. in Lam. & DC., Fl. Franç., ed. 3, 2 (1805) 580. Terrestrial herbs, usually of wet places, sometimes as agricultural weeds. Stems elongate, articulate, usually hollow, originating from a subterranean rhizome, monomorphic or dimorphic; branches absent, solitary, opposite or in whorls, ribbed or striate, usually with hollow internodes, originating from base of foliar sheath. Leaves small, whorled, laterally connected into a toothed, tubular to funnel-form sheath. Sporangiophores peltate, scale-like, forming terminal strobili, these borne on vegetative stems or on achlorophyllous fertile stems (not in Malesia), each sporangiophore bearing 6—9 sporangia in a single row along the underside of the margin. Spores homosporous, globose, bearing 4 long, filiform, cruciately arranged, apically clavate hygroscopic appendages (elaters).