[Marsilea brevipes Nutt. ex A. Br., moreMarsilea fournieri C. Christ, Marsilea longipes Austin, Marsilea mucronata A. Br., Marsilea picta Fée, Marsilea tenuifolia Engelm. apud Kunze, Marsilea uncinata A. Br., Marsilea vestita subsp. tenuifolia (Engelm. ex A. Br.) D.M. Johnson, Marsilea vestita var. mucronata (A. Braun) Bak., Zalusianskya tenuifolia (Engelm. apud O. Kuntze) O. Kuntze, Zalusianskya uncinata (A. Br.) O. Kuntze, Zalusianskya vestita (Hook. & Grev.) O. Kuntze]
Plants forming diffuse or dense clones. Roots arising at nodes. Petioles 2--20 cm, sparsely pubescent. Pinnae 4--19 × 4--16 mm, pubescent to glabrous. Sporocarp stalks erect, unbranched, attached at base of petiole (occasionally up to 3 mm above it), not hooked at apex, 0.5--25 mm. Sporocarps perpendicular or slightly nodding, 3.6--7.6 × 3--6.5 mm, 1.5--2 mm thick, elliptic to nearly round in lateral view, pubescent but soon glabrate, scars left by fallen trichomes often appearing as purple or brown specks; raphe 1.1--1.7 mm, proximal tooth 0.3--0.6 mm, blunt, distal tooth 0.4--1.2 mm, acute, often hooked at apex. Sori 14--22. Sporocarps produced spring--fall (Apr--Oct). Widespread and variable; in ponds and wet depressions and on river floodplains; 0--2300 m; Alta., B.C., Sask.; Ariz., Ark., Calif., Colo., Idaho, Iowa, Kans., La., Minn., Mont., Nebr., Nev., N.Mex., N.Dak., Okla., Oreg., S.Dak., Tex., Utah, Wash., Wyo.; Mexico; South America in Peru. A number of segregate species have been named and recognized in regional floras in North America: Marsilea mucronata A. Braun (less hairy, found east of Rocky Mountains), M . uncinata (glabrous, sporocarp stalks long, distal tooth of sporocarp hooked, south central United States), M . tenuifolia (pinnae very narrow, central Texas), and M . fournieri (small plants and pinnae, southwest). The features upon which these species are based intergrade into one another. The species are therefore best treated as conspecific with M . vestita (D. M. Johnson 1986). Putative hybrids between Marsilea macropoda and this species are discussed under the former.
Rhizome rooting only at the nodes; lfls appressed- hairy on both sides, the emergent ones 5-20 נ5-15 mm, spatulate to flabellate, slightly oblique, at least the inner margin usually concave; peduncle 2-25 mm, usually unbranched, attached at or to 3 mm above the base of the petiole; sporocarp 3.5-7.5 נ3-6.5 mm, the inferior tooth 0.3-0.6 mm, the superior one 0.4-1.2 mm and often hooked; sori 14-22 per sporocarp, with 27-64 microsporangia and (2-)9-15 megasporangia per sorus. Cordilleran region of w. U.S. and adj. Can. and Mex., e. to Minn., Io., and La. (M. mucronata) Ours is the widespread var. vestita.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.