The hybrid nature of Encelia laciniata (Compositae: Heliantheae) and control of population composition by post-dispersal selection

Experimental studies show that the type and most collections of Encelia laciniata are F1 hybrids between E. ventorum and E. palmeri. Other collections referred to E. laciniata are hybrids between E. ventorum and E. asperifolia. Only where the parental species occur together can one find E. laciniata and then it is strictly confined to zones of intermediate habitat or disturbance. Progeny tests show that lack of pollinator fidelity results in many backcross and other recombinant embryos, but these are expressed as mature plants only in direct proportion to the severity of habitat disturbance and are absent altogether from undisturbed sites. Hybrids and their derivatives largely displace the parent species in areas of extreme disturbance. Only extremely intense to absolute post-dispersal selection can account for these phenomena.