Consequences of achene biomass, within-achene allocation patterns, and pappus on germination in ray and disc achenes of Aster umbellatus var. umbellatus (Asteraceae)

Abstract

A familiar floral dimorphism that may have an associated seed heteromorphism, that is, the production of seeds with variable morphologies and ecological strategies, is the presence of both ray and disc florets in the capitula of most Asteraceae. Achenes of Aster umbellatus var. umbellatus Mill. were separated into the ray or disc type with either the pappus remaining attached and intact, or removed. Differential allocation of biomass between ray and disc achenes or heavy and light achenes was not observed. Germination was relatively low (disc achenes with pappus removed, 16.7%; ray achenes with pappus removed, 22.9%; disc achenes with pappus intact, 7.3%; and ray achenes with pappus intact, 7.2%) for each. Although achene weight did not affect the likelihood of germination, germination was 2.5-3 times greater among disc and ray achenes, respectively, for which the pappus was removed as opposed to intact. These results do not conform with previous thoughts relative to the advantageous role of the pappus in germination. As such, I suggest that in this species of Aster the key role of the pappus is to facilitate dispersal as opposed to encourage germination. Furthermore, the production of morphologically and ecologically indistinguishable ray and disc achenes by A. umbellatus var. umbellatus would suggest that the significance of heterogamous capitula, specifically the production of ray florets, rests in their attractiveness of pollinators.Key words: within-achene allocation patterns, germination, Aster.