Genetic and Environmental Effects on Life-History of a Facultative Biennial

Phenology of two populations of Heterotheca subaxillaris, an annual, biennial or perennial species, was recorded in situ and under common garden conditions to know genetic and environmental determinants of their life-history. Bolting date was sizedependent for both populations, larger plants bolted earlier. In both sites, plants bolted throughout the growing season, but the size at which they bolted remaining constant. Flowering date was size-dependent and varied across growing conditions for plants from one site. Plants from the other site flowered uniformly at the end of the growing season. Life-cycle of individuals in this species is thus shown to depend on their genetic origin and environmental conditions.