Opuntia fragilis (Nuttall) Haworth in Illinois: Pad dynamics and sexual reproduction

We studied the sole population of Opuntia fragilis in Illinois for four years, tracking plant and individual pad fates, and investigating flowering success. The population appears to be fairly stable in size from year to year. The fate of a given pad is strongly dependent upon the position of the pad within the plant; basal pads and transitional pads are likely to remain from year to year, while terminal pads experience substantially higher rates of death or fragmentation, and are much more likely to produce new growth and thus become transitional pads themselves. A fungal "black spot" disease, probably a result of winter damage, appears to negatively affect pad survival during some winters but not during other winters. While genetic diversity is not low, flowers do not produce viable seed, even when controlled cross-pollinations are performed, although they are visited by a variety of potential insect pollinators.