Comparative Ecology of Geranium richardsonii and Geranium nervosum

Two perennial species of wild geranium (Geranium nervosum Rydb. and G. richardsonii Fisch. and Trautv. [Geraniaceae] which grow throughout the mountainous regions of western North America were studied to examine the factors influencing the life stage development and the ecological isolation of these two morphologically similar species. Seeds which were produced in the fall reached maximum germination by January for G. nervosum and by March for G. richardsonii. Seeds did not remain viable for more than one winter. Field experiments, coupled with laboratory water stress studies, indicated that G. nervosum seedlings were able to survive in drier environments due to their tap root system. The fibrous root system of G. richardsonii did not extend deep enough in the soil to reach more favorable water potentials. Pollinators distinguish between the Geranium species, thus providing a second isolation mechanism. Hybrids produced from hand crossing did not survive after germination.