Repeated evolution of dioecy from monoecy in Siparunaceae (Laurales)

Siparunaceae comprise Glossocalyx with one species in West Africa and Sipar una with 65 species in the neotropics; all have unisexual flowers, and 15 s pecies are monoecious, 50 dioecious. Parsimony and maximum likelihood analy ses of combined nuclear ribosomal ITS and chloroplast trnL-trnF intergenic spacer sequences yielded almost identical topologies, which were used to tr ace the evolution of the two sexual systems. The African species, which is dioecious, was sister to all neotropical species, and the monoecious specie s formed a grade basal to a large dioecious Andean clade. Dioecy evolved a second time within the monoecious grade. Geographical mapping of 6,496 herb arium collections from all species sorted by sexual system showed that mono ecy is confined to low-lying areas (altitude < 700 m) in the Amazon basin a nd southern Central America. The only morphological trait with a strong phy logenetic signal is leaf margin shape (entire or toothed), although this ch aracter also correlates with altitude, probably reflecting selection on lea f shapes by temperature and rainfall regimes. The data do not reject the mo lecular clock, and branch lengths suggest that the shift to dioecy in the l owlands occurred many million years after the shift to dioecy in the ancest or of the Andean clade.