PLANTS: Aquatic or terrestrial annual (or facultatively perennial) herbs, generally glabrous, with adventitious roots; monoecious or rarely dioecious.
STEMS: delicate, simple or branched, usually 1-4 dm long.
LEAVES: opposite, simple, often polymorphic, estipulate, the margins entire; submerged leaves narrow linear, the apices generally emarginate or bifid, l-nerved; terrestrial and floating leaves obovate to oblanceolate to spatulate, 3- to several-nerved; floating leaves crowded at the ends of the branches forming rosettes.
INFLORESCENCE: of 1-3 sessile flowers in the axils of the leaves.
FLOWERS: hypogynous, inconspicuous, usually subtended by a pair of small, white, falcate or obliquely oval bracteoles; perianth absent.
STAMINATE FLOWERS: consisting of a single stamen on a slender elongate filament.
PISTILLATE FLOWERS: with 2 united carpels; pistil4-lobed (often keeled or winged and apically indented between the lobes), appearing 4-chambered by a false septum, compressed dorso-ventrally; styles 2, slender, often much longer than the ovary.
FRUIT: separating at maturity into 4, l-seeded nutlets. 2n = 6-40.
NOTES: Taxonomically and nomenclaturely difficult because most species are polymorphic.
REFERENCES: Ricketson, Jon. 1995. Callitrichaceae. J. Ariz. - Nev. Acad. Sci. 29(l): 15.
Characters of the family. 35, nearly cosmop.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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