Floral ontogeny in the Plumbaginaceae

Abstract

A scanning electron microscopic study of the floral ontogeny of seven species of the Plumbaginaceae (representing five genera of the Armerioideae and two of the Plumbagoideae) is presented. The early ontogenetic stages in all species examined are sufficiently similar to propose the following familial description. The five sepal primordia are initiated simultaneously or spirally. These soon reach continuity and develop into the synsepalous calyx. Meanwhile, five common stamen-petal primordia that alternate with the sepal primordia are initiated simultaneously on the flattened apex. Soon, two distinct growth-centres can be observed on each of these primordia: a petal primordium at the abaxial side and a stamen primordium on the top. After inception of the common primordia, five gynoecial primordia alternating with the common primordia are initiated simultaneously on the corners of the apex that has become pentagonal. These primordia soon reach continuity and develop into the superior unilocular gynoecium. Continuity between the gynoecial primordia is reached earlier in the Plumbagoideae than in the Armerioideae. In the centre of the ovary a primordium arises that develops into the single basal circinotropous bitegmic ovule. The floral nectaries are associated with the androecium.