Perennial with glabrous vegetative parts (a few hairs on some young lvs); stems ± decumbent, rooting at lower nodes, ascending to c. 60 cm, often very stout and succulent towards base. Lvs sessile, ± amplexicaul, 3-8.5 × 1-2.5-(4) cm, oblong to elliptic or elliptic-ovate, often lanceolate and very membranous when submerged, entire to remotely or occasionally closely serrulate; apex acute. Racemes axillary, opposite, towards ends of shoots, many-flowered, > lvs; peduncle to c. 20 cm long, glabrous or minutely glandular-hairy; pedicels 2-6 mm long, glabrous or minutely glandular-hairy at first, < the linear or linear-lanceolate bracts, but elongating considerably and curving upwards at fruiting. Calyx 3-4 mm long; lobes ovate or ovate-oblong, glabrous, short-acuminate but blunt at tip. Corolla 6-7 mm diam., often whitish with blue veins but appearing bluish mauve, sometimes pinkish mauve. Capsule c. 3 mm wide, suborbicular, somewhat glandular-ciliate. Seeds ovoid to oblong, convex on 1 side, flat on the other.