Aquatic perennial herb; aerial stem 2.5–14 cm tall, simple to much-branched, slender with sessile or stipitate glands above becoming subglabrous; submerged stem up to 1 m long, much branched, glabrous. Leaves on aerial stem usually all verticillate and variously dissected, (2.5–)4–12(–22) mm long, sometimes 2–3 pairs of opposite, undissected, crenate-serrate to lacerate, 1–3-veined leaves towards the apex, up to 15 mm long, 4 mm wide, sessile-glandular to sub-glabrous, rarely all aerial leaves undissected; submerged leaves verticillate in whorls of 6–12, pinnatisect, up to 3 cm long with lobes flattened or capillary. Flowers solitary, axillary, slender pedicellate or very short-pedicellate, appearing sessile; pedicels (0.5–)3.5–10(–15) mm long, sessile-glandular to stipitate-glandular, usually longer than the subtending leaves; bracteoles 2, (1.5–)3–4 mm long, linear to linear-oblong to obovate-lanceolate, acute, entire to irregularly and remotely serrate-dentate to occasionally deeply incised, glandular to subglabrous. Calyx 3.5–6 mm long, sessile-glandular, rarely sparsely hirsute, not striate at maturity; lobes 2–3 mm long, broadly ovate to lanceolate, shortly acuminate, occasionally ciliate. Corolla white to pale yellow or yellow at base of tube, mauve-pink above, (6–)8–12 mm long, externally glabrous; lobes all entire. Stamens with anthers contiguous; posterior filaments 2 mm long, anterior 4 mm long, all glabrous; style up to 4.5 mm long with two lateral processes ± 0.2 mm wide at the apex and below the stigma. Capsule compressed ellipsoid to subglobose, ± 3.4 mm long, dark brown. Fig. 16, p. 43.
