Germination and seed survival in the woody weed, groundsel bush (Baccharis halimifolia L.)

Abstract

Freshly produced achenes of groundsel bush (Baccharis halimifolia L.: Asteraceae) lacked innate dormancy, and fluctuations in temperature and light were necessary to elicit a full germination response. Under conditions of intermittent light, a fluctuation amplitude of less than 1°C was sufficient to promote germination to 50% of its maximal value. Although an increase in the proportion of far-red to red wavelengths inhibited germination under conditions of constant temperature and continuous irradiance, with the introduction of fluctuations in the levels of these factors the inhibiting effect was no longer observed. Germination was minimal at constant temperatures in the absence of light, but the introduction of a 7.5°C temperature fluctuation induced germination in c. 25% of the seed. Under conditions of enforced dormancy brought about through burial, seeds persisted for a minimum period of 2 years.