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United States Department of Agriculture

Agricultural Research Service

Research Project: Aquatic and Riparian Weed Management to Protect U.S. Water Resources in the Far West United States

Location: Exotic and Invasive Weeds Research

Title: Seed size and nutrient content variation for twenty-one invasive and native California and Oregon taxa of the tribe Cynareae (Asteraceae)

Authors
item Spencer, David
item Liow, Pui Sze
item Pitcairn, Michael -
item Villegas, Baldo -

Submitted to: Madrono
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2014
Publication Date: N/A

Interpretive Summary: Invasive plants such as yellow starthistle have spread in western grasslands causing problems for grazing and other land uses. The ability to predict which species will become invasive would aid in prevention and rapid response efforts. One hypothesis is that small seed size may be a good predictor of invasiveness. We tested this hypothesis by measuring seed weight for yellow starthistle and 20 related species, and by performing a growth experiment with 5 species that covered the range of seed sizes within this group. Seed size varied by a factor of 24, from a mean of 1.5 milligrams per seed for yellow starthistle to 35.6 mg per seed for artichoke thistle. However, there were no significant relationships between status as an invasive species and seed size characteristics based on logistic regression analysis. In addition, plant growth rates, photosynthetic rates, leaf area, and leaf chlorophyll content all varied with species, but none of these characteristics was related to seed size. This study demonstrated that for species of thistles, seed size does not predict whether or not the species will become an invasive weed. This information will aid managers in developing the appropriate criteria for predicting plant invasiveness.

Technical Abstract: Seed characteristics are important for seed dispersal, seedling growth, and seedling survival, but there is little information on seed characteristics for several taxa of the tribe Cynareae (Family: Asteraceae). We determined seed characteristics and their variation from natural populations of twenty-one taxa of Cynareae. We also measured C and N content of seeds for seventeen taxa, and conducted a greenhouse growth experiment with five species from this group. Data were used to test the hypothesis that introduced species can be separated from native species based on these characteristics. Seed mass differed significantly (P < 0.0001) among taxa and varied by a factor of 24, from a mean of 1.48 mg for Centaurea solstitialis to 35.63 mg for Cynara cardunculus subsp. flavescens. 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. RGR for greenhouse grown plants ranged from 0.010 to 0.030 g-1 g-1 day-1. Linear regression results indicate that there was no significant relationship between seed mass and RGR or other measures of plant growth and condition and seed mass. For many of the taxa analyzed in this study, the information on seed mass, nutrient content, and growth measures (RGR, net photosynthesis rate) have not been previously reported.

Last Modified: 10/25/2014
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