Clarifying inflorescence homologies and finding new morphological features in the PCK clade (Paniceae): inflorescence development of Panicum maximum and Urochloa plantiginea .

REINHEIMER RENATA; POZNER RAÚL; VEGETTI ABELARDO C.

Congreso; Botany 2004; 2004

A comparative SEM and light microscopy study on inflorescence development in Panicum maximum and Urochloa plantaginea was performed to test whether Panicum maximum should be transferred to Urochloa, and to look for developmental features applicable to future cladistic studies of the PCK clade (P. maximum and some species of Brachiaria, Chaetium, Eriochloa, Melinis and Urochloa). We found that P. maximum and U. plantaginea differ not only in their mature inflorescence structure but also in several fundamental developmental features that exclude P. maximum from Urochloa. Eleven developmental features were found: direction of branch differentiation; development of adventitious buds; apical vs. intercalary development of the main axis; direction of spikelet differentiation; direction of glume, lemma and palea differentiation; position of the lower glume (in some cases); size of the floret meristem; pattern of distal floret development; pattern of gynoecium abortion; differential pollen development between proximal and distal floret; glume elongation; and direction of floret maturation at anthesis. The last six developmental events are related to sex expression. We also found that the main axis of U. plantaginea?s inflorescence is homologous to the first basal internode in the main axis of P. maximum?s inflorescence. The most distal primary branch of U. plantaginea is homologous to the first proximal primary branch in P. maximum. The second and following primary branches (in basipetal order) of U. plantaginea derive from adventitious buds, and they are not homologous to the first most distal primary branch in the same inflorescence. They are also not homologous to any structure in P. maximum?s inflorescence.