Onopordum
Onopordum acanthium - young flowering head
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Asterales
Family:	Asteraceae
Subfamily:	Carduoideae
Tribe:	Cynareae
Genus:	Onopordum
Species
See text.

Onopordum L. is a genus of about 40 species of thistles belonging to the family Asteraceae, native to Europe (mainly the Mediterranean region), northern Africa, the Canary Islands, the Caucasus, and southwest and central Asia. They grow on disturbed land, roadsides, arable land and pastures.

They are biennials (rarely short-lived perennials) with branched, spinose winged stems, growing 0.5-3 m tall. In the first season they form a basal rosette of gray-green felted leaves and rarely a few flower heads. In the second season they grow rapidly to their final height, flowering extensively, and then die off after seed maturation.

The leaves are dentate or shallowly lobed to compound with several pinnatifid or deeply cut leaflets, and strongly spiny.

The terminal flower head is typical for thistles, a semi-spherical to ovoid capitulum 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 capitula have several overlapping rows of leathery basal simple linear-lanceolate spines. These are smooth to slightly pubescent.

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

Onopordum species are used as food plants by the larvae of some Lepidoptera species including Coleophora onopordiella (feeds exclusively on O. acanthium).

Selected species

• Onopordum acanthium L. - Cotton Thistle, Scotch Thistle, Scotch Common-Thistle, Heraldic Thistle, Woolly Thistle
  

  

  Onopordum acanthium - habit
• Onopordum acanthophorum Gand.
• Onopordum acaulon L. - Stemless Thistle, Horse Thistle, Stemless Onopordum
• Onopordum alexandrinum Boiss.
• Onopordum anatolicum (Boiss.) Eig.
• Onopordum anisacanthum Boiss.
• Onopordum arenarium M.Hossain & M.A.A.Al-Sarraf
• Onopordum argolicum Boiss.
• Onopordum armenum Grossh.
• Onopordum bracteatum Boiss. & Heldr.
• Onopordum candidum Nab.
• Onopordum caricum Hub.-Mor.
• Onopordum caulescens d'Urv.
• Onopordum cinereum Grossh.
• Onopordum corymbosum Willk.
• Onopordum davisii Rech.f.
• Onopordum dissectum Murb.
• Onopordum frickii Tamamsch.
• Onopordum heteracanthum C.A.Mey.
• Onopordum humile Loscos
  

  

  Cotton Thistle (Onopordum acanthium) from Thomé Flora von Deutschland, Österreich und der Schweiz 1885
• Onopordum illyricum L. - Illyrian Thistle, Illyrian Cottonthistle
• Onopordum jordanicolum Eig.
• Onopordum laconicum Heldr. & Sart. ex Rouy
• Onopordum leptolepis DC.
• Onopordum macracanthum Schousb.
• Onopordum majorii Beauverd
• Onopordum messeniacum Halácsy
• Onopordum nervosum Boiss. - Moor's Cottonthistle
• Onopordum nivescens Gand.
• Onopordum nogalesii Svent
• Onopordum prjachinii Tamamsch.
• Onopordum sarrafii C.C.Townsend
• Onopordum seravschanicum Tamamsch.
• Onopordum sirsangense Rech.
• Onopordum tauricum Willd. - Turkish Thistle, Taurian Thistle, Taurus Cottonthistle, Bull Cottonthistle
• Onopordum transiens Gand.
• Onopordum turcicum Danin

Natural hybrids

• Onopordum × brevicaule (Onopordum acaulon × Onopordum acanthium )
• Onopordum × erectum (Onopordum nervosum ssp. castellanum × Onopordum tauricum ssp. corymbosum )
• Onopordum × macronervosum (Onopordum nervosum × Onopordum macrocanthum)
• Onopordum × onubense (Onopordum dissectum × Onopordum macrocanthum)
• Onopordum × spinosissimum (Onopordum illyricum × Onopordum acanthium)

[edit] Invasive problems

Some species of Onopordum have been introduced as ornamental plants in the temperate regions of North America and Australia, where they have become naturalised in the wild. 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).^[1] In North America, there are also Trichosirocalus control programs, but they have proved detrimental to native thistles.^[2]

[edit] References

1. ^ Briese, D. T. (2002), "Impact of the rosette crown weevil Trichosirocalus briesei on the growth and reproduction of Onopordum thistles", Journal of Applied Ecology 39: 688, doi:10.1046/j.1365-2664.2002.00747.x 
2. ^ Takahashi, Masaru (2009), "Occurrence of Trichosirocalus horridus (Coleoptera: Curculionidae) on Native Cirsium altissimum Versus Exotic C. Vulgare in North American Tallgrass Prairie", Environmental Entomology 38: 731, doi:10.1603/022.038.0325 

• Briese, D.T., Lane, D., Hyde-Wyatt, B.H., Crocker, J., Diver, R.G. (1990). Distribution of thistles of the genus Onopordum in Australia. Plant Protection Quarterly 5: 23-27.