8b. var. pungens

Stigmas mostly 2. Fruits flattened and unequally biconvex in cross-section (flat on 1 side, rounded on the other). May–September.

Scattered nearly throughout Missouri, but more common south of the Missouri River (U.S. and Canada south to South America and the Caribbean Islands; Europe). Margins of ponds, lakes, sloughs, and ditches, gravel bars, and stream banks, fens, and marshes.

Other characters included by Koyama (1963) and Beetle (1947) do not correlate with the separation of bicarpellate from tricarpellate plants. Of the two varieties, var. pungens is by far the most common in Missouri. In the United States var. pungens is most common in the eastern half, particularly east of the Appalachian Mountains, whereas var. longispicatus predominates in the western half. Missouri is part of a broad zone of geographic overlap between the two varieties, and intermediates (with nearly equal numbers of bicarpellate and tricarpellate florets) have been recorded from areas where both taxa occur. The character of fruit shape can be relatively subtle and easily misinterpreted.