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Rhizomatous colonial perennials with annual or perennial green stems, the epidermis with silicified cell walls and often with regularly arranged silicified projections, so that the surface is minutely rough to the touch. 2n=216 or nearly so. 15, cosmop. Sterile but vegetatively vigorous and persistent hybrids are often produced between species of the same subgenus. Some of these are: E. ×ferrissii Clute = E. hyemale × laevigatum; E. ×litorale Kühlew. = E. arvense × fluviatile; E. ×nelsonii (A. A. Eaton) J. H. Schaffn. = E. laevigatum × variegatum; E. ×trachyodon A. Braun = E. hyemale × variegatum.
Underground stems creeping, freely branching; aerial stems upright, often bearing whorls of branches, usually with a central hollow surrounded by 2 rings of alternating smaller cavities. Lvs in sheathing whorls at the nodes, small and brownish, toothed at the apices. Several sporangia borne on adaxial surface of heads of sporangiophores. Strobili usually terminal on main aerial stems.
Morphological characters and geographic distribution are the same as those of the family.
Characters as for the family.
Characters of the family.
