XVI International Botanical Congess

The C4 photosynthetic pathway is a complex adaptation believed to have at least 31 separate evolutionary origins. The Poaceae and Cyperaceae are the only monocotyledonous families known to use the C4 pathway, each exhibits unique anatomical patterns. We mapped C4 anatomical types onto phylogenetic trees of Cyperaceae constructed using non-molecular and combined molecular and non-molecular data. Cladistic analyses indicate that the C4 pathway has arisen at least four separate times. Anatomical variants have arisen in separate tribes, although there are exceptions. Homoplasy in C4 photosynthetic pathway is indicated by the presence of different anatomical and biochemical variants, and by parallel expression of the same variants. Differences found among anatomical and biochemical types of C4 Cyperaceae, and in other C4 families, indicate that multiple evolutionary events with different developmental patterns have resulted in numerous, eqaually competent variants of the C4 photosynthetic pathway.