Periodicity of seedling emergence and achene survival in some species of Carduus, Cirsium and Onopordum.
Abstract
Achenes of 7 species of Carduus, Cirsium and Onopordum were collected in August-September and mixed with the top 2.5 or 7.5 cm of soil which was then periodically disturbed during 3 or more years. Between 0 and 40% of the achenes produced seedlings in the autumn of sowing. There was wide variation between sowings of the same species in different years, as well as between species. Subsequent seedling emergence was mainly in March-April (Cirsium eriophorum, C. palustre, C. vulgare), April (Carduus acanthoides, C. nutans) or April-May (Cirsium arvense). Onopordum acanthium showed a contrasting pattern; most seedlings appeared in July-September, with small numbers in other months. More than 90% of all seedlings of Cirsium and Carduus spp. that emerged did so within a year after sowing. There were few or none after the second year and very few dormant achenes remained after 5 years. Only about half the achenes of O. acanthium mixed with 7.5cm of soil produced seedlings in the first 16 months. Seedlings continued to appear subsequently and up to 8% of the achenes sown were still dormant and viable after 5 years. From summary.