onopordum

Onopordum is a genus of flowering plants in the family Asteraceae, commonly known as thistles. Species are typically biennial or short-lived perennial herbs with stiff, spiny leaves and tall stems that bear dense heads of purple to pink flowers in summer. The plants are adapted to open, disturbed habitats and dry soils.

Native to Europe and western Asia, Onopordum has been widely introduced elsewhere as ornamentals or escapees and is now naturalized in many regions, including parts of North America, Australia, and New Zealand. They are most common in meadows, pastures, roadsides, and other open habitats.

The best-known species is Onopordum acanthium, the Scotch thistle, a tall plant with woolly, spiny leaves and a stout, bristly stem. Other species occur in drier or more seasonal climates, and collectively the genus includes several dozen taxa.

Life cycle and ecology: Onopordum species usually form a rosette in the first year, then bolt and flower in the second year. They are insect-pollinated, and their seeds are adapted for wind dispersal. They can form dense stands that compete with forage and native vegetation.

Management: In areas where Onopordum is considered invasive or weedy, management focuses on preventing seed production. Methods include mechanical removal, especially before flowering; timely mowing; and herbicidal control with systemic herbicides such as glyphosate in appropriate settings. Integrated approaches may combine grazing and cultural practices to reduce regrowth.