EVOLUTION OF THE TRANSLATOR IN PERIPLOCACEAE AND ASCLEPIADACEAE

This paper deals with the problem of homology between the translators in Periplocaceae and Asclepiadaceae. Since most differences between the flowers in both families are based on the functional differences in the pollination process, it seems that the question of common ancestry can best be solved by clarifying the problem of the evolution of the translator itself. Ontogenetic investigation has revealed that the central element of the periplocoid translator is the adhesive disc together with the base of the stipe. The translator in Secamoneae (the most primitive tribe in Asclepiadaceae) is homologous to this element, and in Secamone the adhesive disc is transformed into the corpusculum while the stipe is represented by the dorsal process to which the pollinia are attached. The translator in the genus Fockea represents an intermediate stage in the further phylogenetic elaboration of the asclepiad translator. It corresponds to Secamone in the development of a dorsal process for the attachment of the pollinia and in the special mode by which the corpusculum is attached to the anther wings. On the other hand, the elongated shape and the formation of a floor in the corpusculum are derived traits pointing to the more highly evolved Asclepiadaceae, such as the Asclepiadeae. The question of the derivation of the caudicles is discussed and a hypothesis concerning their development from pre-adaptive elements in Fockea is put forward. General conclusions are 1. that Periplocaceae and Asclepiadaceae are sister groups and that the common ancestor possessed a primitive translator composed of at least the two elements adhesive disc and stipe; 2. that the morphological difference of the translators between Periplocaceae and Secamone is smaller than between Secamone and the more advanced Aselepiadaceae.