2. Elodea Michx. (elodea, waterweed, bassweed)

(Cook and Urmi-König, 1985)

Plants usually dioecious. Stems sparsely branched or unbranched, 30–200 cm long. Leaves mostly in whorls of 3 or opposite, 6–17 mm long (except at base of stems, where 2–3 mm long), linear to narrowly oblong (narrowly ovate near base of stems), the tips pointed, the margins minutely toothed, without a spongelike mass of enlarged cells on the undersurface. Spathes from the middle and upper leaf axils, the bracts fused along 1 side. Staminate flowers 1 per spathe, sessile or the stalks 3–20 cm long, lacking nectaries, the sepals somewhat boat-shaped, oblong-elliptic, the petals shorter than to about as long as the sepals, sometimes highly reduced, narrower than the sepals, white, oblong to lanceolate, white. Stamens usually 9, the short filaments usually somewhat fused near the base. Pistillate flowers 1 per spathe, on stalks 1–9 cm long, the stalks formed from the elongate tip of the ovary (hypanthium), the sepals and petals slightly shorter than those of the staminate flowers, and with 3 linear staminodes 0.5–0.8 mm long. Styles 3, arching over the petals, white with purple markings, the stigmatic areas entire or 2-lobed. Fruits 5–7 mm long, ovoid to fusiform, beaked, the walls thin and more or less transparent. Five species, native to the New World, but naturalized worldwide.