ABSTRACT
The plants of this family are perennial herbaceous, with underground rhizomes equipped with tubers for storing reserve substances. The stems are articulated, hollow, and rigid due to the impregnation of the external tissue membrane (epidermis) with SiO2. The internodes are ribbed and longitudinally grooved. At the nodes, there are reduced leaves (scales), arranged in whorls and fused together, forming a toothed sheath, with the number of sheath teeth equal to the number of stem ribs. Some species have sterile stems (do not produce sporophylls) and fertile stems. The stems are branched, with branches arranged in whorls. The sporophylls (modified leaves bearing sporangia) have a shield-like peltate shape and form terminal spikes with 5–12 sporangia each. The spores, which are formed in sac-like sporangia, are morphologically identical, while the prothalli formed from them are different (male and female). The spores are surrounded by two long, spiraled, hygroscopic threads that aid in their dispersal. The species in this family are isosporous and heteroprothallian.1- 3
