We collected data from 1998 to 2014 to describe the ecology of the highly endangered Florida scrub plant Crotalaria avonensis (Avon Park Harebells), and herein address several hypotheses based on what was known of its biology and the biology of co-occurring species. This perennial herbaceous legume occurs at 3 sites and prefers microsites with more cover by bare sand than vegetation. The population at an unprotected site has declined in size, but dynamics have been more stable at the 2 protected sites. Marked plants have shown high survival, slow and inconsistent growth, and occasional plant dormancy (usually 1–2 years). Avon Park Harebells is reproductively challenged, with very low rates of fruit set and infrequent visitation by required pollinators. The hardseeded fruits germinated at a rate of 13–56%; the germination speed seemed to increase after scarification, though the overall rate was less than for unscarified seeds. Unscarified seeds remained viable in the seed bank for at least 3 years. Seedlings recruited rarely, had moderate survival, began flowering at 4 years of age or later, and reached the size of median adult plants in 6–8 years. Herbivores affected 7–53% of plants in a given year, but plants showed rapid compensatory resprouting. Caging plants reduced herbivory and increased survival, growth, and flowering. Plants resprouted after fire and mechanical disturbance and exhibited high survival and growth, but repeated disturbances by vehicles caused increased mortality. Avon Park Harebells remains extremely endangered due to its limited range, small population sizes, and poor seedling recruitment. To help this species recover, we recommend fire management, protection from herbivory, introductions and augmentations, and further study of its pollination biology.