Results from reciprocal diallele crossing experiments among a parental generation, as well as a full-sib family of 34 sibs suggests a novel, complex system of self-incompatibility (SI) in Ipomopsis tenuifolia (Polemoniaceae). Thirteen individuals from a population in Baja California, Mexico, were randomly chosen as parental plants. All crosses among parental and F1 individuals were successful, including backcrosses to parents, with the exception of three non-reciprocal crosses in the parental generation. All selfs were incompatible. Pollen tube growth was observed within selfs inside the ovary. The lack of incompatibility among sibships and backcrosses, as well as the complete lack of selfing success may suggest either a multi-locus gametophytic SI system or late-acting SI. Pollen tube growth within the ovary is more consistent with late-acting SI. Thus far, this study does not clarify the discrepancy between previous results of crossing studies in Polemoniaceae. Levinís (1993) results suggested single-locus gametophytic SI in Phlox drummondii, whereas Goodwillie (1997) found sporophytic SI with linear dominance in Linanthus parviflorus. The SI system for Polemoniaceae appears to be more complex than previously thought.

Key words: Ipomopsis tenuifolia , Self-Incompatibility