The reproductive attributes of an endangered plant as compared to a weedy congener

Abstract

Comparisons of reproductive attributes related to fitness can help explain differences in the distribution and abundance of rare and common plant species. This study was conducted to characterize a rare taxon ( Amsinckia grandiflora (Gray) Kleeb, ex Greene) and its widespread congener ( Amsinckia menziesii (Lehm.) Nels. and Macbr. var. intermedia (Fischer and Meyer) Ganders) with respect to major fitness components and variables. These included: (1) inflorescence output (number of inflorescences per plant); (2) floral cache (number of flowers per inflorescence); (3) floral seed cache (number of seeds per flower); (4) seed weight (per 100 seeds); (5) seed output (total number of seeds per plant); and (6) seed yield (total seed weight per plant). All significant correlations among these fitness components were positive. Inflorescence output was the most important variable determining seed output and seed yield for both the rare and common species, whereas seed weight had no significant direct effect on seed output or seed yield. The rare species. A. grandiflora, was especially sensitive to floral seed cache while the common species, A. menziesii var. intermedia, was especially sensitive to inflorescence output. These results are discussed with respect to the evolution of weediness and the conservation of rarities in the native California flora.