Onopordum

Onopordum is a genus of about 50 species of thistles belonging to the sunflower family (Asteraceae).

They are native to Europe (mainly the Mediterranean), Northern Africa, the Canary Islands, the Caucasus, Southwest and Central Asia, and Iraq. They have been introduced as an ornamental plant in the temperate regions of North America and Australia, where they have become naturalised in the wild. They grow on disturbed land, roadsides, arable land and pastures

In most of these countries, these thistles are considered noxious weeds, especially in Australia where a biological control program has been set up (using the Rosette Crown Weevil, Trichosirocalus briesei).

They are biennials or perennials with branched, spinose winged stems, growing as high as 3 m. In the first season they form the leaves and a few flower heads. In the second season they bolt to their final height, blooming extensively, and then die off.

They form a basal rosette of gray-green felted leaves. These dentate or shallowly lobed leaves are strongly spinose. These leaves are compound and consist of several pinnatifid or deeply cut leaflets, or are almost pinnate.

The terminal flower head is typical for thistles: semi-spherical to ovoid with purple (seldom white or pink) disc florets. There are no ray florets. The receptacle is glabrous with dentate margins. The tube of the corolla is slender, sac-shaped and symmetrical. The anthers have awl-shaped outgrowths on the top.

The leathery phyllaries consist of several overlapping rows with simple, linear-lanceolate spines. These are smooth to slightly pubescent.

These plant propagates only by seed. The flowers dry up in mid-summer, releasing their seeds. The fruit is a glabrous achene, 4-6 mm long and with 4 to 50 ribs. The pappus consists of many rows of simple, fine to minutely rough hairs, united in a circular base.

Species