Major events in the evolution of sexual systems in Apiales: ancestral andromonoecy abandoned

Abstract

Schlessmann, M.A.: Major events in the evolution of sexual systems in Apiales: ancestral andromonoecy abandoned. — Plant Div. Evol. 128: 233–245. 2010. — ISSN 1869-6155. Andromonoecy is rare in angiosperms as a whole, but it occurs frequently in Apiales. I investigated the evolution of andromonoecy within Apiales by mapping the known diversity of sexual systems on a phylogenetic tree for the order, and using parsimony and likelihood methods to reconstruct ancestral states. I used the results to test the hypotheses that andromonoecy is ancestral for Araliaceae, Apiaceae, and the entire Apiales. My results indicate that 1) the common ancestor of Apiales was dioecious; 2) the first transition from dioecy to a monomorphic sexual system was to hermaphroditism; and 3) andromonoecy was derived independently several times within the Araliaceae and once in the common ancestor of Myodocarpaceae + Apiaceae. Thus, the ancestral andromonoecy hypothesis should be abandoned for Araliaceae, and for the Apiales as a whole. The sequence in which inflorescence structure, dichogamy, and andromonoecy evolved suggests that interfloral dichogamy, rather than resources available for fruit set or inflorescence structure per se, has been the primary factor promoting the evolution of andromonoecy in Apiales. Similarly, intrafloral dichogamy has been the primary factor determining patterns of staminate flower production by individuals of andromonoe cious taxa.