Floral organogenesis of three species of Jatropha (Euphorbiaceae)

Floral organogenesis of three species of the genus Jatropha L. of the family Euphorbiaceae, viz., J. curcas L., J podagrica Hook. and J gossypifolia L., was studied with scanning electron microscope (SEM). The first sepal primordium is initiated in non-median abaxial position and the second one in median adaxial position. Five sepal primordia arise in a 2/5 sequence on the periphery of the floral apex and are initiated anticlockwise or clockwise in different floral buds of the same species. Five petal primordia initiate simultaneously. There are dicyclic stamens in male flowers with the outer whorl of stamens opposite to the petals (obdiplostemony) and inner whorl opposite to the sepals. Two types of stamen development exist in the genus. In J curcas, belonging to subgen. Curcas, five stamen primordia of the outer whorl arise simultaneously at first and then five of the inner whorl initiate simultaneously. In J podagrica and J gossypifolia, belonging to subgen. Jatropha, eight to nine stamen primordia of the two whorls arise simultaneously. In the female flowers, three carpel primordia appear simultaneously. The flowers of these three species are unisexual. In the female flowers, the ovary bulges and the stamens degenerate, whereas in the male flowers, the stamens grow normally but the ovary is absent. The division of the genus with subgenera is supported by the stamen development.