Centaurea occurs as genus of astir 350-500 metal money of herbaceous thistles and thistle-like flowering plants in the family Asteraceae, mostly native to the Old World. Most common list for different coinage include star thistle, cornflower, knapweed & bluet. A select few mintage come cultivated when ornamental plants in gardens.

Species
Coinage in that genus include: Centaurea calcitrapa – Purple Star Thistle or Caltrop - Europe Centaurea cyanus – Cornflower Centaurea diffusa – Diffuse Knapweed Centaurea iberica Sprengle – A spinous Mediterranean species thought to be a "thistle" mentioned around Genesis Centaurea maculosa Lam. – Spotted Knapweed, an eastern European mintage introduced to the United states, nowadays the pernicious & invasive weed which releases the toxin that reduces incubation of forage metal money. Centaurea montana – Mountain Bluet Centaurea nigra – Black Knapweed or Most common Knapweed Centaurea nigrescens – Tyrol Knapweed - South and Eastern Europe Centaurea repens L. – Russian Knapweed (as well Turkestan Thistle) occurs as perennial, indigen to southern Russia and Asia Minor to Altai and Afghanistan. These are the pernicious weed in area of its native range also when in situ in which it has been inadvertently naturalized. A flower head is lavender within color & non armed using spines. Centaurea scabiosa – Greater Knapweed Centaurea solstitialis L. – A Yellow Star Thistle, shown in the picture in the image below, is an annual that grows to the height of 30-80 cm. This plant is widely naturalized outside of Europe in which these are indigen.

Nectar
Centaurea come copious nectar producers, especially on high-lime soils, and come major honey plants for beekeepers. Star thistle varietal honey is lightly & slightly lemony. These are one of a finest honeys produced in a United states of america, however when these are abundant, a select few of these are fraudulently relabeled & sold when the just, expensive Sourwood honey of the Appalachian Mountains.

A high nectar yield of the genus makes it super attractive to insects such as butterflies and day-flying moths such as Six-spot Burnet. A larvae of some other Lepidoptera species such as The Engrailed and Hummingbird hawk moth use this as a food plant.

Bibliography
Mabberley, D.J. 1987. A Plant Book. The personal lexicon of the higher plants. Cambridge University Click, Cambridge. 706 p. ISBN 0 521 34060 8. Robbins, W.W., M. K. Bellue, & W. S. Ball. 1970. Weeds of California. State of California, Dept. of Agriculture. 547 p.

da:Knopurt (Centaurea) de:Flockenblumen es:Centaurea fr:Centaurea lt:Bajorė nl:Centaurie no:Knoppurt pl:Chaber