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Onopordum acanthium reproduces only by seeds. Most seeds germinate in autumn after the first rains, but some seeds can germinate year round under favourable moisture and temperature conditions. Seeds that germinate in late autumn become biennials. But when they germinate earlier, they can behave as annuals. Buried seed can remain viable in the soil seed bank for at least seven years and possibly for up to twenty years or more. Yearly seed production and seed dormancy are highly variable depending on environmental conditions. The slender and smooth achenes are about 3 mm long and are brown with gray markings. They are tipped with a pappus of slender bristles. Mainly locally dispersed by wind, or more widely by humans, birds, wildlife, livestock or streams, the seeds are sensitive to light and only germinate when close to the surface. Seedlings will emerge from soil depths up to 4. 5 cm, with 0. 5 cm being optimal. While some seeds will germinate in the dark, studies indicate that most germination occurs with alternating light/dark cycles, with 8 hours being the optimal day length.