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Carduus pycnocephalus

Carduus pycnocephalus. Santa Monica Mountains National Recreation Area, California, USA. Taken at Circle X Ranch: Grotto Trail. NPS photo

Classification System: APG IV

Superregnum: Eukaryota
Regnum: Plantae
Cladus: Angiosperms
Cladus: Eudicots
Cladus: Core eudicots
Cladus: Asterids
Cladus: Campanulids
Ordo: Asterales

Familia: Asteraceae
Subfamilia: Carduoideae
Tribus: Cardueae
Subtribus: Carduinae
Genus: Carduus
Species: Carduus pycnocephalus
Subspecies: C. p. subsp. albidus – C. p. subsp. cinereus – C. p. subsp. intermedius – C. p. subsp. marmoratus – C. p. subsp. pycnocephalus

Carduus pycnocephalus L., Sp. Pl. ed. 2, 2: 1151. 1763.

Carduus pycnocephalus Spreng. = Carduus cephalanthus Viv.


Linnaeus, C. 1763. Species Plantarum, ed. 2, Tomus II: 1151. Reference page.


Hassler, M. 2018. Carduus pycnocephalus. World Plants: Synonymic Checklists of the Vascular Plants of the World In: Roskovh, Y., Abucay, L., Orrell, T., Nicolson, D., Bailly, N., Kirk, P., Bourgoin, T., DeWalt, R.E., Decock, W., De Wever, A., Nieukerken, E. van, Zarucchi, J. & Penev, L., eds. 2018. Species 2000 & ITIS Catalogue of Life. Published online. Accessed: 2018 Apr. 19. Reference page.
International Plant Names Index. 2018. Carduus pycnocephalus. Published online. Accessed: Apr. 19 2018.
The Plant List 2013. Carduus pycnocephalus in The Plant List Version 1.1. Published online. Accessed: 2018 Apr. 19. 2018. Carduus pycnocephalus. Missouri Botanical Garden. Published online. Accessed: 19 Apr. 2018.
USDA, ARS, Germplasm Resources Information Network. Carduus pycnocephalus in the Germplasm Resources Information Network (GRIN), U.S. Department of Agriculture Agricultural Research Service. Accessed: 07-Oct-06.

Vernacular names
English: Italian thistle, Italian plumeless thistle, Plymouth thistle
español: Cardo borriquero, cardo negro
suomi: Balkaninkarhiainen
italiano: Cardo saettone

Carduus pycnocephalus, with common names including Italian thistle, Italian plumeless thistle, and Plymouth thistle,[1] is a species of thistle. It is native to: the Mediterranean region in southern Europe, North Africa, and Western Asia; East Europe and the Caucasus; and the Indian Subcontinent.[2]

The plant has become an introduced species in other regions, and on other continents, often becoming a noxious weed or invasive species.

Carduus pycnocephalus plant (California).

A winter annual, Carduus pycnocephalus stems range from 8 inches (20 cm) to 6.6 feet (2.0 m), and are glabrous to slightly wooly. The multiple stems are winged with spines.[3]

The plant grows in a rosettes of 10–14 inches (25–36 cm) in diameter, with four to ten lobed basal leaves that are 4–6 inches (10–15 cm) long. Cauline leaves are tomentose on the underside and contain spines on the lobe tips.[3]

Flower heads are 2-5 per cluster, densely matted with cobwebby hairs at the base of the phyllaries and spiny towards the tips. Corollas are pink to purple, approx. .4-.6 in (1-1.4 cm) long, and the fruits are brown to gold, with a bristly, minutely barbed pappus.[3][4][5]
Noxious weed
Dense crowding by Italian thistle rosettes.

Carduus pycnocephalus has become a noxious weed in Australia, New Zealand, Macaronesia, South Africa, the Arabian Peninsula, South America, Hawaii, and North America, especially in much of California.[2][6] It is a C-listed weed by the California Department of Agriculture and a Moderate Invasive Plant rating by the California Invasive Plant Council.[7] It favors grasslands, woodlands, and chaparral vegetation types, but is especially prevalent in oak woodlands in and around the Central Valley. It is found in disturbed areas, often with basaltic soils, fertile soils, or soils with a relatively high pH (> 6.5).[5][7]

Italian thistle can grow densely, crowding out other vegetation with dense rosette 'colonies' in the winter, thereby preventing establishment of native plants. Its spiny leaves, stems, and phyllaries prevent animals from grazing on it and nearby forage.[8][9] Its tendency to grow under the canopy of oaks increases the risk of wildfire damage to the trees, as fire can more easily spread to the canopy.


Mechanical methods can be effective but must be done before the plant sets seed. Additionally, the root must be severed at least 4 inches (10 cm) below the ground to prevent the plant from regenerating.[8] Mowing and slashing are not reliable as the plant is able to regrow and produce seed even at a height of 3 inches (7.6 cm).[5][10]


Biological control agents have limited success with Carduus pycnocephalus. Insects that tested host-specific by the California Dept. of Agriculture and caused significant damage to the reproductive structures of the Italian thistle have not been utilized, due to concerns about possible predation of California's native thistle species.[11] Puccinia cardui-pycnocephali is a species of rust (fungus) apparently exclusive to Carduus pycnocephalus.[8] Other rust species have been found on Italian thistle as well.[8][12][13]

Grazing by sheep or goats (not cattle) in Australia has showed promise as well.[14]


Chemical control can be achieved with a variety of products including: Clopyralid, glyphosate, Diquat, Picloram, and 2, 4-D ester. However, caution must be exercised when using these products, and their use is not always appropriate, especially near water surfaces and other sensitive natural habitats.[5][8] Check with local, regional, and national regulations directing use.

BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
"Carduus pycnocephalus". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2013-04-08.
U.S. National Park Service: Invasive Non-Native Plants in Sequoia and Kings Canyon National Parks — Italian Thistle
Jepson; Hickman 1993
Bossard, CC., J.M. Randall, and M. Hoshovsky. (eds.); Invasive Plants of California’s Wildlands; University of California Press, Berkeley, CA; 2000.
Cal-IPC—California Invasive Plant Council species treatment: Carduus pycnocephalus . accessed 4.8.2013
Mattole Restoration Council: Italian Thistle (Carduus pycnocephalus) . accessed 4.8.2013
Parsons 1973
Tasmania Dept. of Agriculture 1977
Sheppard et al. 1991
Olivieri 1984
Bruckart 1991
Bendall 1973

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