Osmundaceae Martinov

Plants terrestrial, with mostly unbranched, often massive, erect, or shortly creeping, ascending, sometimes treelike trunk clothed in roots and persistent stipes, hairy at apex. Rhizome anatomy distinctive, an ectophloic siphonostele (with a pith of parenchyma in center and phloem outside of vascular cylinder only), with a ring of discrete xylem strands, these often conduplicate or twice conduplicate in cross section. Fronds 1-or 2-pinnate, catadromous, when young bearing wool-like, uniseriate hairs, these deciduous or persistent at axes, dimorphic or with fertile portions dissimilar to sterile; stipe caespitose, spirally arranged, with laterally winged stipules at bases, bearing mucilaginous hairs when young, with a single U-shaped vascular bundle; sclerenchyma strongly developed; base of lateral pinnae nearly always distinctly articulate (but only functional in some species); pinnule base sometimes also articulate, though less distinctly so; veins free, subpinnately furcate. Sporangia not assembled in sori, following veins or entirely covering strongly contracted fertile segments, sporangia large, with 128-512 spores, opening by an apical slit, annulus lateral; spores green, subglobose, trilete; gametophytes large, green, cordate, surficial. x = 22.