1. Egeria densa Planchon, Annales des Sciences Naturelles, Botanique. sér. 3, 11: 80. 1849.
Stems 1--3 mm diam. Leaves whorled, recurved, 10--40 ´ 1.5--4.5 mm. Staminate spathes 2--4-flowered, 7.5--12 mm; pedicel to 80 mm. 2n = 46.
Flowers summer--fall. Shallow waters of lakes and streams; introduced; 0--500 m; introduced; Ala., Ark., Calif., Colo., Del., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Mass., Miss., Mo., N.J., N.Mex., N.Y., N.C, Okla., Oreg., Pa., S.C., Tenn., Tex., Vt., Va., W.Va.; Mexico; West Indies; Central America; native, South America; Europe; Africa; Asia; Australia.
Egeria densa is native to southeastern Brazil and has been widely sold in the aquarium trade, often becoming established in nature. Only staminate plants of E. densa have been observed outside its native range. Reproduction, then, occurs entirely by vegetative methods. No differentiated vegetative reproductive structures (turions, bulbils, etc.) are known (C. D. K. Cook and K. Urmi-König 1984b); however, the species is known to live temporarily under ice. The leaves of Egeria densa, which are only two cell-layers thick, are much used to demonstrate plant-cell structure and cytoplasmic streaming in introductory botany courses.