Genera in the tribe Cardueae (Asteraceae) include both non-invasive and invasive species widely dispersed in the western U.S. Seed characteristics are important for seed dispersal, seedling growth, and seedling survival. We determined seed characteristics and their variation from natural populations of 22 taxa of Cardueae. We also measured C and N content of seeds for 17 taxa, and conducted a greenhouse growth experiment with five species from this group. We tested the hypothesis that it is possible to distinguish invasive species from non-invasive species based on these characteristics. Seed weight differed significantly (P < 0.0001) among taxa and varied by a factor of 24, from a mean of 1.48 mg for Centaurea solstitialis L. to 35.63 mg for Cynara cardunculus L. subsp. flavescens Wiklund. There were no significant relationships between status as an invasive species and explanatory variables based on logistic regression results (P > 0.05). Seed N, C, and C∶N ratio differed significantly (P < 0.0001) among taxa, but these characteristics were not associated with invasiveness. Relative growth rate (RGR) for greenhouse grown plants ranged from 0.010 to 0.030 g g−1 day−1. Linear regression results indicate that there was no significant relationship between seed weight and RGR or other measures of plant growth and condition and seed weight. For many of the taxa analyzed in this study, the information on seed weight, nutrient content, and growth measures (RGR, net photosynthesis rate) have not been previously reported.
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Vol. 61 • No. 4