1. Marsilea Linnaeus, Sp. Pl. 2: 1099. 1753; Gen. Pl. ed. 5, 485, 1754.
Water-clover, pepperwort [for Count Luigi Marsigli (1656--1730), Italian mycologist at Bologna]
David M. Johnson
Plants aquatic or amphibious, forming diffuse or dense colonies. Roots arising at nodes, sometimes also on internodes. Leaves deciduous in temperate regions, heteromorphic, floating leaves averaging larger than land leaves. Petiole filiform, stiffly erect or procumbent in land leaves, lax in floating leaves. Blade palmately divided into 4 pinnae. Pinnae cuneate or obdeltate, pulvinate at base, frequently with numerous red or brown streaks abaxially in floating leaves. Sporocarps borne on branched or unbranched stalks at or near bases of petioles, aboveground (except in Marsilea ancylopoda ), attached laterally to stalk apex (attached portion called raphe), tip of stalk often protruding as bump or tooth (proximal tooth), some species also with tooth distal to stalk apex (distal tooth); sporocarps densely to sparsely hairy, less so with age, dehiscing into 2 valves.
Ca. 45 species (6 in the flora with 5 native, 1 introduced): nearly worldwide.
Species identification is virtually impossible without fertile material. The common name water-clover refers to the resemblance of the leaves to those of clover ( Trifolium spp., Fabaceae); pepperwort refers to the sporocarp, which approximates a peppercorn in size and shape.
Johnson, D. M. 1985. New records for longevity of Marsilea sporocarps. Amer. Fern J. 75: 30--31. Johnson, D. M. 1988. Proposal to conserve Marsilea L. (Pteridophyta: Marsileaceae) with Marsilea quadrifolia as typ. conserv. Taxon 37: 483--486.