Floral meristic and organogenetic variation was sampled in Ruppia occidentalis from an alkaline lake of the Nebraska Sandhills and in Ruppia maritima var. rostrata from a saline, non-Sandhills lake nearby. The androecium is meristically stable, always having two stamens, but the gynoecium is not. Seventy-two percent of the flowers of R. maritima had four carpels and the others had three, and in 80% of inflorescences the two flowers had the same number. In about one-third of inflorescences having dissimilar carpel numbers, the four-carpellate flower was uppermost. The number of carpels in each flower of R. occidentalis ranged from four to nine, averaging six, and in 57% of inflorescences both flowers had the same number; of those that did not, most had more in the lower than upper flower. Twenty-five percent of the flowers had four carpels, 8% had five, 35% had six, 15% had seven, 14% had eight, and 3% had nine. Ordered, dimerous, decussate organogenesis through the first four carpels followed the same pat...