Ecophysiology of Seed Germination and Flowering in Common Broomweed, Amphiachyris dracunculoides (DC) Nutt

Abstract

Common broomweed (Amphiachyris dracunculoides (DC.) Nutt.) behaves both as a winter and as a summer annual. Seeds germinate in either autumn or spring, and the life cycle is completed the following autumn. Seeds were nondormant at maturity, and 48 to 94% of them germinated in light at daily thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20 degrees C, but 42% or less germinated in darkness at these temperatures. Thus, a high percentage of the seeds dispersed in early autumn germinate within a few days in warm soil if soil water is not limiting. With late autumn dispersal, however, germination of a high percentage of the seeds is delayed until spring. Vernalization was not required for flowering, and both vernalized and nonvernalized plants flowered under long and short photoperiods. However, plants from vernalized seeds required fewer days to flower under both photoperiods than did plants from nonvernalized controls. Additionally, plants vernalized in the seed and/or seedling stages did not form a rosette prior to shoot elongation, whereas plants not vernalized in the seed or seedling stages formed a rosette.