Floral development and homeosis in Saraca (Leguminosae: Caesalpinioideae: Detarieae)

Floral development was compared in two species of Saraca in caesalpinioid tribe Detarieae: Saraca declinata, with four stamens, and Saraca indica, with seven stamens. The inflorescences are paniculate corymbs of helically arranged floral bracts, with a single bracteolate flower in each bract axil. The paired bracteoles are large, persistent, and showy. Floral symmetry is radial at anthesis. Flowers initiate in successive acropetal order in an inflorescence and undergo anthesis in the same order. The first sepal is initiated abaxially and nonmedianly. Floral development is helical in the calyx and in the second whorl and unidirectional in the third whorl (where present). Members of the second and third whorl become stamens. Overlap in the time of initiation occurs (1) between the sepal primordia (the first whorl) and members of the second whorl and (2) between primordia of the second and third whorl, where both are present. The carpel initiates after the second whorl is initiated. Both species show organ fusion (two sepals), organ suppression (some or all stamens), loss of organs (antepetalous stamens), and homeosis (stamens in petal sites). This is the first reported example of homeotic conversion of petal primordia into stamens in a legume flower. The calyx appears tetramerous as a result of the fusion of the two adaxial sepal primordia. In late development, zonal growth produces a hypanthial tube and a disk with petals and stamens along the rim, and the carpel base becomes realigned to the adaxial side of the hypanthial tube.