Perennial herb with herbaceous rootstock emitting erect (wholly submerged) to prostrate and rooting (terrestrial) stems up to 0.4(- 0.7) m, the terrestrial or shallow-water shoots bearing erect to ascending, terminal and axillary flowering shoots 0.05-0.2 m tall, the whole emergent plant up to sepals (dorsal) crisped-pubescent to tomentose or inflorescence puberulous, submerged parts shortly and finely villous to glabrous. Stems green to reddish, terete, 1 mm thick and threadlike (submerged) to 6 mm thick with swollen spongy internodes (shallow water or terrestrial); internodes up to 50(-80) mm long and 5 x as long as leaves (deep water) to shorter than leaves (terrestrial). Leaves sessile; lamina 5-30 x 2-22 mm, oblong-elliptic (deep water) to broadly elliptic or broadly ovate or orbicular, concolorous, not glaucous, plane, spreading; apex rounded, base cuneate (deep water) to cordate-amplexicaul; venation: 2-3 pairs of laterals curved-ascending from base or near base of midrib; tertiary reticulation dense, plane; laminar glands pale, dense, scattered, small; intramarginal glands pale, dense. Inflorescence 1-13-flowered from one node, terminal but usually apparently axillary when only one of uppermost pair of axillary shoots develops, laxly subcorymbiform to narrowly pyramidal, without lower flowering branches; pedicels 3-7 mm (-11 mm in fruit); bracts not auriculate; bracteoles triangular, obtuse, red-glandular-ciliate. Flowers 7-15 mm in diam., infundibular to subrotate, pseudo-tubular; buds cylindric to narrowly ovoid, subacute. Sepals 2.5-3.5 x 1-2 mm, subequal, c. 0.3-0.5 united, ovate or triangular-ovate to narrowly oblong, rounded, with margin glandular-ciliate; veins 3(5), branched or not; laminar glands pale, linear; marginal glands red, on short cilia. Petals lemon yellow, not tinged red, 8-10 x 2.7-3 mm, c. 3 x sepals, oblong-oblanceolate, subtruncate, without apiculus, in lower 0.25 with adnate ligulate appendage, apex free, trifid; laminar and marginal glands absent. Stamens 12-13, clearly 3-fascicled, with filaments c. 0.65 connate with line of hairs below free parts, longest c. 5-6.5 mm, c. 0.6 x petals; anther gland amber; lodicules 3, squamiform, 0.5 x 0.25 mm, elliptic, retuse. Ovary 1-locular, c. 2.5-2.7 x 1-1.5 mm, narrowly ovoid; styles 3, 2-2.5 mm, just shorter than ovary, narrowly outcurving. Capsule 4-5 x 2.5-3 mm, ovoid to cylindric, exceeding sepals. Seeds dark yellow-brown, 0.6-0.8 mm long; testa ribbed-scalariform (cf. Reynaud, 1985: 91, t. 2 ff. 3, 4).