Potamogetonaceae

Abstract

Perennial or rarely annual floating-leaved or submersed glabrous herbs growing in fresh or brackish waters, sometimes stranded by receding water levels. Roots fibrous, few, nonseptate, from lower nodes of stems. Stems slender, branched or unbranched, often dimorphic, the lower stems rhizomatous or stoloniferous, occasionally with tubers, the upper erect, leafy, the tips often modified into turions. Leaves alternate and the upper 2–12 subopposite, or opposite throughout, entire to serrulate, sessile, or petiolate, 1-many-veined, mostly ligulate; ligules forming a tubular sheath around the stem, free from or adnate to the base of the blade; veins when several or numerous parallel or arching, often connected by cross-veins; axillary infravaginal scales present, membranous; submersed leaves thin, linear to orbicular; floating blades often leathery, lanceolate to elliptic or ovate. Inflorescences pedunculate, axillary, or terminal, with 2 opposite flowers or more than 2 flowers in a capitate to interrupted spike, with a subtending spathe. Flowers perfect, hypognous, actinomorphic; tepals 4(−2), in one series, distinct, rounded, flat to convex, short-clawed, greenish, reddish, or brownish. Stamens 4, rarely 2–3; anthers extrorse, 2-locular, dehiscing by longitudinal slits; filaments adnate to the perianth claw; pollen grains shed singly, spherical. Gynoecium of (1−) 4 (−7) distinct carpels, the carpels unilocular, sometimes with an indistinct stipe; ovules solitary, attached to the ventral margin of the carpel; styles short; stigmas capitate. Fruits usually drupelets with a membranous exocarp, fleshy mesocarp, and stony endocarp, or rarely berries, opening by decay of the pericarp. Seeds solitary, exalbuminous, with coiled embryo.