Coronas, outgrowths of the corolla and/or stamens, are prominent structures in the flowers of many Apocynaceae sensu lato. Their extreme positional and morphological variability has made primary homology assessment of mature structures very difficult both across the family as a whole and within more recently diverged groups. The genus Dischidia R. Br., ca. 80 species, is characterized by membranous, dorsiventrally flattened staminal corona segments, each consisting of a stalk and a bifid blade with recurved arms, but there is such diversity in the genus that homology of the full range of mature structures cannot be assessed with confidence. Development of staminal coronas in 12 species of Dischidia, encompassing a large fraction of the morphological diversity in the genus, was studied with SEM. Staminal coronas occur alone or in combination with two additional structures, here termed dorsal and basal staminal appendages. Development of the typical staminal corona segment can be divided into five modules: 1) primordium initiation, 2) primordium differentiation, 3) arm primordium formation, 4) stalk elongation, and 5) blade differentiation. Two distinct types of primordia, here termed plate and bilobed primordia, develop during module 2; however their subsequent development results in some very similar mature morphologies. Different blade morphologies are generated by differential growth and post-genital fusion during module 5. Additional diversity results from non-execution of one or more of the modules, although a primordium is always initiated. Nineteen developmental and morphological characters were identified, allowing detailed comparison of the full range of coronas in the genus. Cladistic analysis of these characters in combination with other morphological characters and sequences of the second intron of LEAFY indicates that the bilobed primordium is an unreversed synapomorphy, while elimination of later modules has evolved independently at least twice.

Key words: Dischidia , Apocynaceae, corona, development, flower, phylogeny