The ecological life cycle of the cedar glade endemic Leavenworthia exigua var. exigua

Abstract

Field, laboratory, and greenhouse studies were conducted on the ecological life cycle of the cedar glade endemic Leavenworthia exigua var. exigua over a 2-year period. Leavenworthia exigua var. exigua completes its life cycle (seed to seed) during autumn, winter, and early spring and is in the dormant seed stage from midspring to early autumn. This winter annual type of life cycle strategy is an adaptation of the species to its summer-arid, winter-wet habitat.Seeds of L. exigua var. exigua exhibit true dormancy at maturity and dispersal in spring. The seeds gradually afterripen during the spring–summer rest period. During the afterripening period the seeds pass from true (innate) dormancy to relative (conditional) dormancy then to a state of non-dormancy. After entering relative dormancy the temperature range for germination is widened through an increase of the maximum temperatures over which germination can occur. By early autumn most of the seeds in a population are completely non-dormant and can germinate over a wide range of temperatures, including those that normally occur in early autumn in its habitat. The exact time of germination in autumn is controlled by soil moisture. This type of afterripening pattern and germination control is an adaptation of the species to a hot, dry season.Although flower buds are formed during late autumn and early winter, the low temperatures and short photoperiods that accompany the winter season are not required for flower bud initiation and subsequent flowering. The main effect of low winter temperature on L. exigua var. exigua is that it slows growth and development and thus delays flowering and fruiting until early spring.