REPRODUCTIVE BIOLOGY OF ASTER CURTUS (ASTERACEAE), A PACIFIC NORTHWEST ENDEMIC

Aspects of the reproductive biology of Aster curtus were investigated to shed light on the current rarity of the species, which is endemic to grasslands of western Washington and Oregon. A bagging experiment showed that excluding insect pollinators significantly decreased the production of viable seeds. Where insects were allowed access, seed production by this perennial forb was not unusually low. Seeds of A. curtus exposed to light germinated over a wide range of temperatures, but few seeds germinated in the dark. Stratification improved germination. Aster curtus was shown to be a stress‐tolerant species that grows very slowly under all conditions. Although seed production and germination do not appear to limit A. curtus , competition from other species probably restricts seedling recruitment in undisturbed communities. Habitat loss due to agriculture, urban expansion, and the natural conversion of grasslands to Douglas fir forests appears to be a more important reason for the historic loss of A. curtus populations.