Queen of the prairie, Filipendula rubra (Rosaceae), is a clonal plant species inhabiting calcareous fens and wet meadows of the northcentral United States. F. rubra reproduces asexually by underground rhizomes and sexually by seed. While many studies have explored genotype diversity in clonal species with limited sexual reproduction, fewer have been conducted on clonal species with the potential for extensive sexual reproduction. We studied the relationship between the extent of sexual reproduction and genotype diversity. Although genotype diversity in F. rubra was double that reported by others for 27 nearly obligate clonal plant species, it was still quite low. For 25 populations studied, the mean number of genotypes was 5.5 (range = 1–15; SE = 0.964) and the average proportion of distinguishable genotypes was 0.38 (range = 0.03–1.00; SE = 0.07). The production of viable seed was quite variable among populations (mean proportion of viable seeds = 0.242; range = 0.002–0.565; SE = 0.04). Considering that some inflorescences can produce over 5,000 seeds, the potential for recruitment of sexually produced individuals is very large. No correlation was found between seed production and genotype diversity as was expected in a self‐incompatible species in which one‐third of the populations possessed a single genotype. It was hypothesized that the low genotype diversity found in numerous populations may be due to competition limiting recruitment of new seedlings.

Queen‐of‐the‐prairie, Filipendula rubra (Rosaceae), is a perennial, rhizomatous herb restricted to calcareous fens, spring seeps, and wet prairies, and is distributed in the northcentral United States from Iowa to New York. Because of the scarcity of adequate habitat, F. rubra is a rare and endangered species in several states. At Botkin Fen and other fens in Missouri, F. rubra possesses limited sexual reproduction. A study was conducted to determine causal mechanisms of its limited seed production that may be barriers to establishing this rare and endangered species in other fens in Missouri. A genetic‐ecological hypothesis was supported. F. rubra was found to be self‐incompatible. At Botkin Fen, most inflorescences produced very few seeds because most (85.4%) belonged to a single clone. Pollinators (Lassioglossum sp.) had a high probability of transporting pollen with the same self‐incompatibility alleles. A few genetically different clones did produce significant quantities of seed. However, this seed, with its significant pool of genetic variability, was not recruited into the population. Apparently, competition from the dense sedges and grasses prevented the establishment of new seedlings.

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