XVI International Botanical Congess

Investigations of floral anatomy of the monocot family Pontederiaceae revealed several characters of systematic importance. These include crystal type, tannin cell type and distribution, floral aerenchyma distribution, septal nectary occurrence, and other characters relating to ovary structure. We found traditionally described placentation types to be inadequate and propose a re-definition to include aspects of septal fusion, placenta position, placenta type, and ovule row number. A cladistic analysis using these new data reveals a different interpretation of evolution. Comparative cladistic analyses using traditional versus revised terminology show differences in topology and robustness of phylogenetic trees. Similar studies may be valuable for other angiosperm groups.