Thistle-like plants, typically biennial, with spiny, white hairy, leaves and stems. In summer, topped with many purple flowerheads. Can be tall and statuesque, with our native O. acanthium being a good example of this.
The numerous small flowers that make up the large flowerheads are outstandingly attractive to all manner of pollinating insects, especially honeybees, bumblebees, leaf-cutter bees, butterflies and hoverflies. The foliage is also palatable to the larva of several lepidoptera, including the thistle ermine moth and painted lady butterfly. Furthermore, in autumn the seeds are devoured by finches, especially goldfinches and linnets.