Differences between males and females of Cirsium arvense (L.) Scop. in morphology and sexual performance are described. No functional pollen was observed in females, and no pollen-sterile anthers were observed in males. The difference between the sexes in ovule functions is not absolute however: some males produce occasional fruits. The number and distribution of fruits on both sexes are described. The fruits borne on males are smaller and germinate less well than those borne on females, but the seedlings from the two sexes grow equally well. On the average, males contribute only 5.3 × 10−4 as many genomes via ovules as do females. The average male constancy, the proportion of male genes transmitted via pollen, is estimated as 0.9989. The primary sex index, a measure of the functional approach to strict dioecy (represented as 1.00) is 0.9995. C. arvense is described as near-dioecious and varying from dioecy in a gynodioecious manner. The opinion expressed by Correns that the near-dioecy of C. arvense has been derived from hermaphroditism via gynodioecy is upheld.
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Lloyd et al. (1976) studied this question.