Carduus is a genus of flowering plants in the family Asteraceae, and the tribe Cardueae, one of two genera considered to be true thistles, the other being
Cirsium. Plants of the genus are known commonly as
plumeless thistles. They are native to temperate Eurasia and North Africa, and several are known elsewhere as introduced species. This genus is noted for its disproportionately high number of noxious weeds compared to other flowering plant genera.
Etymology: The genus name
Carduus is from the Latin for "a kind of thistle" or "thistlelike plant". It is related to the word
Cardonnacum ("a place of chardons or thistles"), which is the origin of Chardonnay, the name of the grape variety. It is also related to the word
card, which as a noun means a device (often a stiff-bristled brush) for aligning and cleaning fibers, and as a verb means the action of processing fibers in that way.
These are usually annual or biennial herbs, sometimes perennial. Species often grow 2 meters in height but are known to reach 4 meters. The erect stems are winged and spiny, and usually have woolly hairs. The leaf blades are hairy to hairless and entire or divided into lobes, and they have spine-toothed edges. The flower heads are solitary or borne in inflorescences of up to 20. The head is spherical to cylindrical and covered in several layers of spreading or curving spine-tipped phyllaries. It contains long, tubular disc florets in shades of white, pink, or purple. The fruit is a cypsela tipped with a pappus of barbed bristles or scales.
Ecology: Several
Carduus are notorious invasive plants outside their native range, for example, in Australia and the United States. Species such as
C. acanthoides,
C. nutans,
C. pycnocephalus, and
C. tenuiflorus easily become weedy in disturbed habitat, such as overgrazed pasture.
C. nutans is allelopathic, producing compounds that inhibit the growth and development of other plants.
Agents of biological pest control that have been used against weedy
Carduus thistles include the thistle head weevil (
Rhinocyllus conicus), thistle crown weevil (
Trichosirocalus horridus), and thistle crown fly (
Cheilosia corydon). The musk thistle rust (
Puccinia carduorum), a fungus, may also be used against
C. nutans.
Species: The genus includes 82 accepted species, and several natural hybrids.
- Carduus acanthocephalus
- Carduus acanthoides – spiny plumeless thistle
- Carduus acicularis
- Carduus adpressus
- Carduus affinis
- Carduus amanus
- Carduus angusticeps
- Carduus × aragonensis
- Carduus argentatus
- Carduus argyroa
- Carduus × arvaticus
- Carduus asturicus
- Carduus × atacinus
- Carduus aurosicus
- Carduus axillaris
- Carduus baeocephalus
- Carduus ballii
- Carduus × bergadensis
- Carduus bourgaei
- Carduus bourgeanus
- Carduus broteroi
- Carduus × brunneri
- Carduus budaianus
- Carduus × camplonensis
- Carduus candicans
- Carduus × cantabricus
- Carduus carduelis
- Carduus carlinoides
- Carduus carpetanus
- Carduus cephalanthus
- Carduus chevallieri
- Carduus chrysacanthus
- Carduus clavulatus
- Carduus collinus
- Carduus corymbosus
- Carduus crispus – curly plumeless thistle, curled thistle, welted thistle
- Carduus dahuricus
- Carduus defloratus
- Carduus edelbergii
- Carduus × estivali
- Carduus × fallax
- Carduus fasciculiflorus
- Carduus fissurae
- Carduus getulus
- Carduus × gillotii
- Carduus × grassensis
- Carduus × grenieri
- Carduus hamulosus
- Carduus hazslinszkyanus
- Carduus hohenackeri
- Carduus ibicensis
- Carduus × intercedens
- Carduus × ipe
- Carduus × jordanii
- Carduus kerneri
- Carduus kirghisicus
- Carduus kumaunensis
- Carduus lanuginosus
- Carduus × leptocephalus
- Carduus leptocladus
- Carduus litigiosus
- Carduus lobulatus
- Carduus lusitanicus
- Carduus macrocephalus
- Carduus malyi
- Carduus maroccanus
- Carduus martinezii
- Carduus membranaceus
- Carduus meonanthus
- Carduus × meratii
- Carduus × mixtus
- Carduus modestii
- Carduus × montis-majoris
- Carduus × moritzii
- Carduus myriacanthus
- Carduus nawaschini
- Carduus nervosus
- Carduus nigrescens
- Carduus numidicus
- Carduus nutans – musk thistle, nodding thistle
- Carduus olympicus
- Carduus onopordioides
- Carduus × orthocephalus
- Carduus peisonis
- Carduus personata
- Carduus poliochrus
- Carduus × puechii
- Carduus pumilus
- Carduus × pycnocephaloformis
- Carduus pycnocephalus – Italian thistle, Italian plumeless thistle, compact-headed thistle
- Carduus pycnocephalus subsp. albidus
- Carduus pycnocephalus subsp. arabicus (synonym Carduus arabicus ) – Arabian thistle
- Carduus pycnocephalus subsp. breviphyllarius
- Carduus pycnocephalus subsp. cinereus
- Carduus pycnocephalus subsp. intermedius
- Carduus pycnocephalus subsp. pycnocephalus
- Carduus quercifolius
- Carduus ramosissimus
- Carduus rechingerianus
- Carduus rivasgodayanus
- Carduus santacreui
- Carduus × schulzeanus
- Carduus seminudus
- Carduus × sepincola
- Carduus × septentrionalis
- Carduus solteszii
- Carduus spachianus
- Carduus squarrosus
- Carduus × stangii
- Carduus tenuiflorus – sheep thistle, shore thistle, slender thistle
- Carduus × theriotii
- Carduus thracicus
- Carduus tmoleus
- Carduus transcaspicus
- Carduus × turocensis
- Carduus uncinatus
- Carduus × veronensis
- Carduus × vigoi
- Carduus volutarioides
- Carduus × weizensis
Formerly placed here: - Afrocarduus afromontanus (as Carduus afromontanus )
- Afrocarduus keniensis (as Carduus keniensis )
- Carduus keniensis × C. platyphyllus
- Afrocarduus kikuyorum (as Carduus kikuyorum )
- Afrocarduus leptacanthus (as Carduus leptacanthus )
- Afrocarduus macracanthus (as Carduus macracanthus )
- Afrocarduus millefolius (as Carduus millefolius )
- Afrocarduus nyassanus (as Carduus nyassanus )
- Afrocarduus ruwenzoriensis (as Carduus ruwenzoriensis )
- Afrocarduus schimperi (as Carduus schimperi )
- Afrocarduus silvarum (as Carduus silvarum )