Synchrony and Periodicity of Flowering in Frasera Speciosa (Gentianaceae)

Synchronized flowering in populations of Frasera speciosa occurs at 2—4 yr intervals. In the East River Valley, Gunnison County, Colorado, major flowering years were 1969, 1973, 1977, and 1980; flowering occurred in alternate years at the highest site (3750 m). Some flowering in three populations in other years suggests that environmental factors can influence the periodicity of flowering. Frasera flowers are preformed at least 3 yr in advance of flowering, although the causes of floral initiation and subsequent synchronous flowering over broad areas are not clear. Progeny of a single plant produced in the same year may grow at different rates and flower over an extended period at different sizes. For Frasera this provides an alternative to iteroparity or seed dormancy as a means of persisting in an unpredictable environment. Both the increase in seed—set and the lowering of seed predation among Frasera individuals in dense neighborhoods have probably provided the selective basis for the evolution of periodic synchronous flowering.