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Keywords:

  • Cirsium arvense;
  • dioecy;
  • hermaphrodites;
  • seed-set;
  • pollen and ovule contributions

Summary

Cirsium arvense (L.) Scop. has been thought to be completely or almost completely dioecious, with clear morphological and functional differences between males that set an average number of less than 0.1 viable seeds per capitulum and females that produce no pollen. An investigation of three populations in southern Britain showed that 15 % of the clones with polleniferous ‘male’ flowers were in fact hermaphrodite, with high or fairly high seed yields (10 to 65 seeds per capitulum) and a further 11 % were subhermaphrodites with seed yields of 2 to 10 seeds per capitulum. The flowers and capitula of the hermaphrodites and subhermaphrodites closely resembled those of typical male clones at the flowering stage, but their fruiting capitula ranged from typically male to typically female in appearance. The mean size and weight of the seeds set on hermaphrodites and subhermaphrodites were similar to those of seeds set on females, and seed viability was high in most hermaphrodites and subhermaphrodites. Some hermaphrodites had higher seed yields per capitulum than the overall mean for females. Pollen output per flower was lower in hermaphrodites than in typical males, but pollen from hermaphrodites was fertile and gave high seed-set when used to pollinate female flowers. Hermaphrodites were self-fertile, although seed-sets on selfing were relatively low. In the hermaphrodites, the pollen contribution relative to that of typical males ranged from 0.24 to 0.85, and the ovule contribution relative to that of pure females ranged from 0.13 to 1.29.