The Breeding System of Oxalis squamata,a Tristylous South American Species

Oxalis squamata is a perennial endemic herb of the Chilean-Argentine Andes previously reported as a distylous species. In this paper, analysis of floral morphology, incompatibility relations and population structure show that O. squamata possesses morphological and functional tristyly. The three floral morphs differ in calyx and corolla length, style and stamen length, pollen grain size and stylar pubescence. Results of hand pollinations showed the presence of a strong incompatibility system. Legitimate pollinations with the L and M morphs as seed parents produced approximately equal numbers of seeds per pollination. The S morph produced less than half the number of seeds per legitimate pollination compared to the other two morphs. Intra- and intermorph illegitimate pollinations produce almost no seeds. Morph representation in the population was isoplethic. Fruit and seed production did not differ significantly for the three morphs in the population. Comparison of experimental and natural production of fruits and seeds suggests that seed set in the natural population may be pollen-limited for the L and M morphs.