We studied the relationships between self-incompatibility mechanisms and floral parameters in the genus Hypochaeris L. sect. Hypochaeris (consisting of H. glabra, H. radicata, H. arachnoidea, and H. salzmanniana). We assessed at intra-and interspecific levels (1) the self-incompatibility (SI) mechanism and its distribution among populations, (2) the relationship between SI and floral parameters, and (3) the relationship of SI to reproductive success. Hypochaeris salzmanniana is

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... , H. glabra is self-compatible, and H. arachnoidea and H. radicata are self-incompatible. Floral parameters differed among populations of H. salzmanniana: plants in self-compatible populations had fewer flowers per head, a smaller head diameter on the flower, and a shorter period of anthesis than self-incompatible populations. We also detected this pattern within a semi-compatible population of H. salzmanniana, and these differences were also found between species with different breeding mechanisms. Fruit to flower ratio in natural populations was generally high (.60%) in all species, regardless of breeding system. It is hypothesized that self-compatibility may have arisen through loss of allelic diversity at the S locus due to bottleneck events and genetic drift.