Click on the image below to view an
expanded illustration for this species.
Amphibious perennial herb, usually with stolons and rooting from nodes, roots slender, fibrous; stems decumbent to prostrate, creeping, to 50 cm long, simple to few branched, smooth or sparsely stiff short-hairy, somewhat hollow.
Tufted at nodes, simple, lanceolate or oblanceolate to thread-like, 0.7-6.5 cm long, 0.4-10 mm wide, usually entire, sometimes shallowly-toothed, bases and tips pointed to thread-like; long- to short-stalked.
Inflorescence of solitary, terminal flowers or few-flowered cymes near branch tips, on stalks to 10 cm long; bracts lanceolate or oblanceolate, receptacle smooth; petals 5 or 6, distinct, yellow, 2.5-7 mm long, 1-4 mm wide, egg-shaped, nectary on upper surface, the nectary scale smooth, shallowly cup-shaped, wider than long; sepals 5, spreading or weakly bent back, 1.5-4 mm long, 1-2 mm wide, smooth or appressed stiff-hairy; stamens 10-50; pistils 5-50.
Achenes, several to many in a globe-shaped head 2-4 mm long, 3-4 mm wide, the achenes egg-shaped, 1.2-1.6 mm long, 1-1.4 mm wide, smooth, smooth to net-veined; beaks persistent, lanceolate to linear, straight or curved, 0.1-0.6 mm long.
Separation of this species into infraspecific taxa, based mainly on leaf width and flower size, is arbitrary at best. See Calder and Taylor (1968) and Whittemore (1997) for alternative treatments.