Herbs 20-100 cm high from a thin creeping rhizome, forming slender winter-buds. Stems with long internodes below, short above, grooved, producing numerous fairly short side branches above. Leaves dimorphous; submerged leaves alternate, translucent, soft, linear to narrowly linear-lanceolate, 3-7 cm long and 1-3 mm broad, apex acute or acuminate, the area between the midrib and lateral nerves consisting of lacunar, reticulated tissue with larger cells, the lateral nerves becoming faint towards the tip, approaching the midrib gradually; upper floating "involucral" leaves opposite, just below the flowering spikes, lanceolate to oblong-lanceolate, up to 2 cm long and 5 mm broad, narrowed into a petiole of 1 cm long, thinly coriaceous, not transparent, apple green, with about 7 nerves showing up disÂtinctly below (some leaves showing transiÂtional stages from the submerged to the floating forms); stipular sheaths convolute, small, soon decaying, upper somewhat larger and broader. Spikes small, 25-40 mm long, lengthening during fruiting, whorls 3-7, each whorl usually 2-flowered, scape flattened, slightly thicker above, about 15 mm long. Fruit about 2 mm long and 1 • 5 mm broad, rounded to oblong in outline, broad-shoulÂdered above, tapered to the base, ventral keel nearly straight, with a central tooth, dorsal keel crenulate ending in a distinct tooth, lateral keels convex ending in teeth near the base, beak fairly long and broad, upturned. Fig. 16 : 1.
