Output and dispersal of propagules of Carduus acanthoides L

Summary: Propagules of Carduus acanthoides are pappus‐bearing achenes. Flower production, potential achene output, seedbank and wind dispersal of propagules of Carduus acanthoides were analysed. Flower production was measured in four cohorts in 1986–87 and three cohorts the following reproductive season, when the potential achene output was estimated. Achene output was very large in all cases but early cohorts had a longer fruiting period and produced more flowers and fruits per plant. The seedbank was small and results from autumn and spring samples showed a low seed persistence in soil. In laboratory experiments greater landing and dispersion distances were reached at higher wind speeds, the major wind effect being that on the movement of propagules after landing. Barriers simulating vegetation almost completely stopped this movement after landing and the final distances reached were almost the same at all wind speeds. In field experiments achenes recovered in seed traps and seedling emergence show the same pattern of distribution around the parent plant. The implication of these results for the behaviour of thistle populations are discussed.