Relationship of Breeding System to Rarity in the Lakeside Daisy ( <i>Hymenoxys acaulis var. glabra</i> )

The breeding system of a rare Great Lakes endemic, the lakeside daisy ( Hymenoxys acaulis var. glabra ), was investigated when plants from a remnant Illinois population produced no seeds for over 15 years. To determine if the Lakeside daisy was self‐incompatible, 20 plants from two populations, Illinois and Ohio, were selfed and outcrossed. Seed/ovule ratios were compared among the different treatments and the location of the incompatibility reaction was identified. Lakeside daisy was found to be self‐incompatible (sporophytic). The last Illinois population was effectively extinct because the remaining plants belonged to the same mating type ( N e = 1) and only produced seeds when outcrossed to the Ohio plants. Cross‐incompatibility was also observed among Ohio plants, suggesting that within large populations, compatible mating types may be rare locally. In addition, inbreeding depression (lower seed/ovule ratios in inbred than in outcrosses) was observed after one generation of inbreeding. Small populations of self‐incompatible species are vulnerable to extinction if the number of self‐incompatibility alleles, either as a result of a bottleneck or of genetic drift, falls below tbe number needed for the breeding system to function. Recovery protocols based on these genetic considerations were developed and implemented in 1988 when Lakeside daisy populations were established at three Illinois nature preserves.