Aquatic herbs, with diœcious or polygamous regular flowers, sessile or on scape-like peduncles from a spathe, and simple or double floral envelopes, which in the fertile flowers are united into a tube and coherent with the 1–3-celled ovary. Stamens 3–12, distinct or monadelphous; anthers 2-celled. Stigmas 3 or 6. Fruit ripening under water, indehiscent, many-seeded. Seeds ascending, without albumen; embryo straight.
Tribe I. HYDRILLEÆ. Stem elongated, submerged, leafy. Spathes small, sessile.
1. Elodea. Leaves verticillate (rarely opposite). Perianth-tube long-filiform.
Tribe II. VALLISNERIEÆ. Stemless. Leaves elongated. Spathes pedunculate.
2. Vallisneria. Submerged; grass-like. Fertile flower solitary on a very long scape.
Tribe III. STRATIOTEÆ. Stem very short, with crowded leaves. Spathes pedunculate. Ovary 6–9-celled.
3. Limnobium. Stemless, floating; broad leaves long-petioled.
1. ELODÈA, Michx. Water-weed.
Flowers polygamo-diœcious, solitary and sessile from a sessile tubular 2-cleft axillary spathe. Sterile flowers small or minute, with 3 sepals barely united at base, and usually 3 similar or narrower petals; filaments short and united at base, or none; anthers 3–9, oval. Fertile flowers pistillate or apparently perfect; perianth extended into an extremely long capillary tube; the limb 6-parted; the small lobes obovate, spreading. Stamens 3–9, often with imperfect anthers or none. Ovary 1-celled, with 3 parietal placentæ, each bearing a few orthotropous ovules; the capillary style coherent with the tube of the perianth; stigmas 3, large, 2-lobed or notched, exserted. Fruit oblong, coriaceous, few-seeded.—Perennial slender submerged herbs, with elongated branching stems, thickly beset with pellucid and veinless, 1-nerved, sessile, whorled or opposite leaves. The staminate flowers (rarely seen) commonly break off, as in Vallisneria, and float on the surface, where they expand and shed their pollen around the stigmas of the fertile flowers, raised to the surface by the prolonged calyx-tube, which varies in length according to the depth of the water. (Name from ἑλώδης, marshy.)
1. E. Canadénsis, Michx. Leaves in 3's or 4's, or the lower opposite, varying from linear to oval-oblong, minutely serrulate; stamens 9 in the sterile flowers, 3 or 6 almost sessile anthers in the fertile. (Anacharis Canadensis, Planchon.)—Slow streams and ponds, common. July.