XVI International Botanical Congess

Homomorphic self-incompatibility (SI) mechanisms have been found to show family constancy and this may have useful predictive value. Other breeding systems occur sporadically across families, probably as a consequence of repeated, independent evolution. The Malvales show diverse breeding systems but mainly of the non-constant type, i.e. dioecy, heteromorphic SI and apomixis, and differential self vs. cross pollen tube growth also seems important in promoting outbreeding in the Malvaceae. Current literature indicates a lack of homomorphic SI in this Order, with some possible exceptions, e.g. Dombeya species, but a new study supports possible SI in a species of Luehea, also Sterculiaceae. The enigmatic 'late-acting SI' or 'ovarian sterility' shows sufficient examples in the Bombacaceae and Sterculiaceae to suggest the occurrence of a phyletic cluster for this phenomenon.