This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Perennial or annual herbs with long-petioled, elliptic, ovate or lanceolate often cordate or sagittate leaves, 3-9-ribbed and mostly punctate with dots or lines. Scapes often longer than the leaves; inflorescence racemose or paniculate, the flowers verticillate, each verticil with 3 outer bracts-and numerous inner bracteoles; flowers perfect; sepals 3, distinct, persistent; petals white, deciduous; receptacle large, convex or globose; stamens 12-30; ovaries numerous; style obliquely apical, persistent; stigma simple; fruit achenes, more or less compressed, coriaceous, ribbed and beaked, forming spinose heads. [Greek, in allusion to the spinose heads of fruit.]
Scapes reclining or prostrate: style shorter than the ovary; beak of achene short.
Scapes erect; style longer than the ovary; beak of achene long.
Sagittaria radicans Nutt. Trans. Am. Phil. Soc.
(II.) 5: 159. 1833-37. Echinodorus radicans Engelm. in A. Gray, Man.
Ed. 2, 438. 1856.
Leaves coarse, ovate, obtuse, cordate, 2'-8' long, 1 1/2'-7 1/2 wide, marked with short pellucid lines, nerves 5-9; cross-veins netted. Petioles sometimes 20' long; scapes creeping, 2°-4° long, scabrous, often rooting at the nodes; verticils distant; bracts linear-lanceolate, acuminate, dilated at the base; pedicels 3-12, unequal, l'-2 1/2' long, slender; sepals persistent, shorter than the heads; petals larger, obovate, about 3" long; stamens about 20; style shorter than the ovary; achenes numerous, about 2" long, 6-10-ribbed, with 2-several oval glands on each side and beaks about one-fourth their length; fruiting heads 4" in diameter.
Alisma cordifolia L. Sp. PI. 343. 1753. Echinodorus rostratus Engelm. in A. Gray, Man.
Ed. 2, 538. 1856. Echinodorus cordifolius Griseb. Abh. Kon.
Gesell. Wiss. Gott. 7: 257. 1857. Echinodorus cordifolius lanceolatus Mack. &
Bush; Fl. Jackson Co. 10. 1902.
Leaves various, ovate, obtuse, cordate, 6'- 8' long and wide, in smaller plants sometimes lanceolate, acute at each end, 1'-2' long; petioles angular, striate, i'-io' high; scapes 1 or more, erect, 5'-16' tall; flowers 3-6 in the verticils; pedicels \'-\' long, erect after flowering; bracts linear-lanceolate, acuminate, dilated at the base; sepals shorter than the heads; petals 2"-3" long; stamens often 12; styles longer than the ovary; fruiting heads bur-like, 2"-3" in diameter; achenes 1 1/2" long, narrowly obovate or falcate, 6-8-ribbed; beak apical, half the length of the achene.
In swamps and ditches, Illinois to Florida, west to Missouri and Texas. Also in tropical America. June-July.