The spikelet is the basic floral unit in the Cyperaceae, and spikelets of the Cyperaceae are described as racemose in all but the most primitive tribes. Flower number, floral sex, and distribution of sexes in spikelets have been important characters in suprageneric classifications. Descriptions of spikelet characteristics for sawgrass, Cladium jamaicense Crantz, however, vary among authors. I analyzed spikelet morphology using developmental, morphological and phenological studies of individuals in one ex situ and three natural sawgrass populations in south Florida, U.S.A. Sawgrass spikelets have two flowers that mature in succession. All flowers are developmentally hermaphroditic and have a single gynoecium with typically three stylar branches and an androecium of two stamens. When flowers mature as hermaphrodites, they are protogynous. The first flower to expand (F1) terminates the spikelet axis, while the second flower to mature (F2), develops in the axil of the last bract produced on the spikelet axis. Thus, the spikelet is cymose. In 86% of the flowers from three populations the gynoecium of the F1 flower aborted, so this flower was functionally male and the spikelet was protandrous. In 13% of the remaining individuals, however, the F1 flower was hermaphroditic. The F2 flower was typically hermaphroditic. In a protandrous spikelet the male F1 flower released pollen in a day. Maturation of the F2 gynoecium occurred two to four days later, followed by expansion of the F2 stamens in one to two days. Spikelets on an inflorescence expanded synchronously. This data indicates that spikelets in C. jamaicense are dichogamous both within flowers and between flowers in a spikelet, while spikelet sex expression can vary among plants and populations.

Key words: Cladium jamaicense, cymose, dichogamy, protogyny, sawgrass, spikelet morphology