THE BREEDING SYSTEM OF OXALIS SUKSDORFII

The Pacific Coast species Oxalis suksdorfii (section Corniculatae) is morphologically tristylous. Flowers of the 3 kinds of plants present in natural populations differ in style length, stamen length, pollen size, stigma size and orientation, and stylar pubescence. Experimental studies and field observations indicate that plants with long-styled flowers are weakly self-compatible and show little differentiation in size or compatibility relationships of pollen from the 2 sets of stamens. Plants with mid-styled flowers have strongly differentiated pollen, but produce few capsules or seed after any artificial or natural pollinations. Plants with short-styled flowers are self-incompatible and show slight pollen differentiation. The data presented suggest that O. suksdorfii approaches functional dimorphism since the mid-styled form contributes little pollen and few seeds in sexual reproduction. The species may be in the process of losing the mid-styled form completely and provides a model of certain physiological and morphological changes which may have accompanied elimination of the mid-styled form in other Oxalis species. The abundance of plants with mid-styled flowers in natural populations suggests, however, that this form may be retained because it contributes to general population fitness, or because the genetic control of heterostyly in this species prevents its elimination.