Flower and spikelet morphology in sawgrass, Cladium jamaicense Crantz (Cyperaceae)

In recent systematic treatments of the Cyperaceae, spikelets of all but the most primitive tribes have been considered to be indeterminate, whereas historically the number of flowers, floral sex and distribution of sexes in spikelets have been important characters in suprageneric classifications. However, descriptions of these spikelet characteristics for sawgrass, Cladium jamaicense Crantz, vary among authors. Spikelet morphology was analysed using developmental and phenological studies of sawgrass populations in south Florida, USA. Sawgrass spikelets have two flowers that expand successively. Flowers are fundamentally hermaphroditic and protogynous. The first flower to expand (F1) terminates the spikelet axis, whereas the second flower (F2), ensheathed by an addorsed prophyll, develops in the axil of the last bract produced on the axis. In 86 % of the spikelets examined from ramets of three populations, the gynoecium of the F1 flower aborted, so this flower was functionally male and the spikelet was protandrous. However, in 14 % of spikelets from these individuals, the F1 flower was hermaphroditic and could set seed. The F2 flower was typically hermaphroditic and matured stigmas, then anthers. Thus, spikelets in C. jamaicense are determinate and have two flowers that are dichogamous both within flowers and between flowers in a spikelet; spikelet sex expression can vary among plants and populations, especially in the first flower. These data for sawgrass suggest that a re-examination of spikelet development and phenology in other genera is needed to clarify the expression of these characters in the family. (C) 2002 Annals of Botany Company.