Annual, with large floating stem, rooting at the nodes. Leaves floating, lamina 2.5-7.5 (-10) cm long, 2-8 mm broad, orbicular, cordate at base, with conspicuous dense brown glands on the under surface, margin entire or wavy, petiole (C.5) 1-5 cm long, Pedicel 0.5-5 cm long. Calyx lobes 3-4 x c.2 mm, oblong, rounded. Corolla lobes oblong, acute, c.4 x 1.5-2 mm, white, with yellow base and longitudnal folds along the margin and centre. Stamens 2.75-3 mm long; anthers c. 1 mm long. Capsule ellipsoid, 5-6 mm long, 10-20 seeded. Seeds c. 1 mm long. tuberculate.