Elodea densa Casp.

Perennial, aquatic herb, permanently submerged. Leaves always in whorls of 3 or 4, sessile, serrulate, terminating in a single spine. Inflorescence in axil of foliage leaves; spathe sessile, of 2 united bracts. Flowers unisexual, arising from spathes situated in upper leaf axils; each flower with a thread-like hypanthium; sepals 3; petals 3, large, 2-3x longer than sepals and alternating with them. Male flowers 2 or 4, held above water surface on rigid pedicels; sepals green; petals white; stamens 9, 3 central, erect and opposite sepals, outer 6 in 2 whorls of 3; pistillodium 3-lobed, green. Female flowers solitary; elongated hypanthium bearing flower above water surface; ovary of 3 carpels; enclosed in base of hypanthium; styles 3, flattened.

Can be grown by divisions.