Distribution and Habitat
Cotton thistle is native to Europe and Asia. The plant prefers habitats with dry summers, such as the Mediterranean region, growing best in sandy, sandy clay and calcareous soils which are rich in ammonium salts. It grows in ruderal places, as well as dry pastures and disturbed fields. Its preferred habitats are natural areas, disturbed sites, roadsides, fields, and especially sites with fertile soils, agricultural areas, range/grasslands, riparian zones, scrub/shrublands valleys and plains along with water courses. Temperature and moisture, rather than soil nutrient concentrations determine the ecological performance of Onopordum species.
In Europe, the plant tends to colonize disturbed pastures. In its native range, Cotton thistle is considered a weak competitor that needs regeneration gaps to develop and maintain stands; populations tend to retreat when disturbance ceases. The plant has been widely introduced at mid-latitudes across much of North America.
Cotton thistle can spread rapidly. For example, it was first found in Utah in 1963. By 1981, it covered approximately 6070 hectares in 17 counties. Eight years later, it had spread to cover more than 22,540 hectares in 22 counties.
Read more about this topic: Onopordum Acanthium
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