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Brittle prickly pear; Phytogeography


We surveyed the distribution of Opuntia fragilis ( Nutt.) Haw. in Steam County, MN, where it is restricted to a few rock outcrops. To compare the populations within three sites, we mapped clusters of pads and measured each individual pad within each cluster. Pads tended to be located in a narrow band of shallow soil between the bare rock and the angiosperm-dominated plant communities growing on adjacent deeper soils. Significant differences existed between the three populations in pad widths, average pad cluster sizes, and pad appearances. Although several pads flowered, none of the flower set seed, indicating that persistence of these populations probably occurs primarily via asexual reproduction.

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