Variation in summer dormancy in the lilioid geophyte Burchardia umbellata (Colchicaceae).

Plant dormancy is a form of phenotypic plasticity that minimizes exposure to seasonally stressful conditions. We examined variation in summer dormancy in two highland and two lowland populations of the lilioid geophyte Burchardia umbellata to test the prediction that facultative dormancy is advantageous in habitats with variable summer conditions. Consistent with this prediction fewer highland plants than lowland plants became dormant under wet common garden conditions. Also, significant among-family variance occurred within highland but not lowland populations, indicating genetic differences among and within populations. Most lowland plants became dormant when exposed to wet or dry conditions (∼92%), indicating that dormancy was primarily obligate. In contrast, dormancy in highland plants increased from 44% under wet conditions to 93% under dry conditions, indicating that dormancy of some highland plants was facultative and induced by drought. Survival, growth, and flowering were reduced in lowland populations, and in dormant vs. nondormant highland plants, indicating costs of dormancy that could negate the advantages of dormancy under variable summer conditions. Summers in lowland populations are predictably hot and dry, favoring a phenotype that responds invariably to environmental cues that are correlated to future dry conditions. In highland populations, variable summer conditions probably maintain polymorphism in dormancy.