An Illustrated Flora of the Northern United States, Canada and the British Possessions/Alismaceae
Fl. Franc. 3: 181.
Aquatic or marsh herbs, mostly glabrous, with fibrous roots, scapose stems and basal long-petioled sheathing leaves. Inflorescence racemose or paniculate. Flowers regular, perfect, monoecious or dioecious, pedicelled, the pedicels verticillate and subtended by bracts. Receptacle flat or convex. Sepals 3, persistent. Petals 3, larger, deciduous, imbricated in the bud. Stamens 6 or more; anthers 2-celled, extrorse or dehiscing by lateral slits. Ovaries numerous or rarely few, 1-celled, usually with a single ovule in each cell. Carpels becoming achenes in fruit in our species. Seeds uncinate-curved. Embryo horseshoe-shaped. Endosperm none. Latex-tubes are found in all the species, according to Micheli.
About 13 genera and 65 species, of wide distribution in fresh water swamps and streams.
|•||Carpels borne in one series; achenes verticillate.||1.||Alisma.|
|•||Carpels borne in several series; achenes capitate.|
|•||Style not apical; fruit-heads not echinate; achene turgid, obscurely beaked.||2.||Helianthium.|
|•||Style apical; fruit-heads echinate; achene flat, prominently beaked.||3.||Echinodonts.|
|•||Flowers polygamous, monoecious or dioecious.|
|•||Lower flowers of the inflorescence perfect.||4.||Lophotocarpiis.|
|•||Lower flowers of the inflorescence pistillate.||5.||Sagittaria.|