Scientific Name: Cynara cardunculus
Common Name: Artichoke Thistle, Cardoon
Spiny thistle of the sunflower family
Head high, occasionally taller, crowned by a cluster of showy, bright purple thistle flowerheads
Stems are leafy, branched, stout
Can be 5-6 feet in height and 5 feet in diameter
Has a large perennial tap root
Blue and purple flowering stems
Bright purple thistle flowerheads 2-3 inches in diameter from April to July
Rarely patches of white-flowering plants are found
One to several stout flower stalks rise up to five feet in diameter
Solitary composite flowering heads have spiny phyllaries and showy purple disk flowers
Basal leaves are deeply lobed and gray-green
Four feet in length
Smaller leaves grow from the flower stalk as it extends upwards
Large thorny leaves
Habitat & Basic Biology (life history, dispersal abilities):
Spreads only by seed
Seeds separate easily and quickly from the thistle down, usually not more than 66 feet from the parent plant
Strong winds may pile up great banks of thistledown against fence lines and road margins
Birds feeding could knock seeds to the ground
Water and gravity carry seeds short distances on slopes
Seeds may attach to mammals and spread along game trails in coastal sage scrub in southern California
Germinates in December-July
Flowers in April and into July throughout its range
In a year of average rainfall in San Diego, a mature plant can produce more that 12 flowerheads with as many as 200 seeds per head. In dryer years, plants are smaller.
Growth is rapid during cool and wet winter months in coastal and southern California
Grows naturally in harsh habitat conditions (arid region) with high temperature, elevated salinity and drought in summer
Came to US in the 1800s as the cultivated eduble cardoon.
Functional traits (photosynthetic rates, phenology, etc.):
Herbaceous perennial plant
Higher photosynthetic rates than their native neighbors
Different seed size and structure disperse differently, which in turn may alter germination and establishment patterns throughout the seed shadow.
Distribution (geographic range):
Native to the Mediterranean and Naples, Italy
Became widespread on over 150,00 acres of California rangeland as well as in Australia, New Zealand, and South America on grazing lands
Found in disturbed areas up to 1,650 feet throughout the state
Common in annual rangelands, especially with coastal influence
Found inland in disturbed grasslands or abandoned agricultural fields
Worst concentrations of the plant were found in Orange, Solano, and Contra Costa Counties
Locally dense populations in the Coast Ranges, Central Valley, and Sierra Nevada foothills
Has been observed colonizing riparian woodlands and natural openings in chaparral and coastal sage scrub, growing under willow, mulefat, and sycamore, as well as in native grasslands
Does well in soils with a heavy clay content
Yearly monitoring and repeat eradication are necessary because it is able to resprout after chemical spraying and is able to build up a seedbank that lasts 5 or more years
Eradication is the most effective when mature plants are bolting
Chemical control efforts are successful on sizable populations in several open space parks and on military lands managed for their natural resources
Hand grubbing, root plowing by tractors, displacement planting, and applying herbicide 2,4-D from airplanes or helicopters
Decapitation of flowers and seed heads prior to maturity to reduce total seed production and most valuable in slowing the spread of the plant in areas where herbicide spraying was not possible at the time
Foliar application of 2% glyphosate (Round-Up Monsanto) during the active growth period (January-July)
Evolution (of traits in novel range):
In combination with the naturally robust growth properties of thistles world wide, evolutionary selection of agricultural disturbance in the Mediterranean and Middle East, gave rise to the genetic potential to become highly selective weeds.
Came to US in mid 1800s as the cultivated edible cardoon. Escape from cultivation resulted in a reversion to many of this cultivar’s aggressive and wild characteristics. The result of its evolution is an invasive plant that shares vegetative and reproductive characteristics with the world’s worst weeds
Performance of invader in CA (interactions with species native to S. CA):
Associated with overgrazing
Invaded over 150,000 acres in 31 counties
Reduces forage production and limits movement of livestock
The stout, upright, spreading nature of the plant and high densities make wildlife movement difficult
Outcompetes native vegetation with its aggressive root system
Also competes with natives for light, water, and nutrients
At high densities, it becomes a monoculture that excludes shrubs, herbaceous plants and annual grasses
It mainly displaces annual exotic grasses
List of References:
Calflora: Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals, including the Consortium of Calif. Herbaria. [web application]. 2014. Berkeley, California: The Calflora Database [a non-profit organization]. Available: http://www.calflora.org/ (Accessed: Jun 06, 2014).
“Cynara Cardunculus (artichoke Thistle).” Cynara Cardunculus. Cal-IPC, n.d. Web. 06 June 2014.
The California Invasive Plant Council provides a comprehensive profile overview of invasive species.
Falleh, H., Ksouri, R., Chaieb, K., Karray-Bouraoui, N., Trabelsi, N., Boulaaba, M., & Abdelly, C. (2008). Phenolic composition of Cynara cardunculus L. organs, and their biological activities. C.R. Biologies, 331, 372-379.
This study compared phenolic contents and antioxidant activity in C. cardunculus L. organs.
Kelly, M., Pepper, A. (1996). Controlling Cynara Cardunculus(Artichoke Thistle, Cardoon, etc.). California Exotic Pest Plant Council, 1-5.
Pepper and her associates describe control methods for C. cardunculus, funded by the California Exotic Pest Plant Council.
Khaldi, S., Sonnante, G., & Gazzah, M. (2012). Analysis of molecular genetic diversity of cardoon (Cynara cardunculus L.) in Tunisia. C.R. Biologies, 335, 389-397.
Sonnante and colleagues show that microsatellites are effective tools for plant species characterization and the analysed populations have a high genetic variability and will be suitable as genetic stocks for conservation and sustainable utilization programs of Cynara cardunculus L. in Tunisia.
Marushia, R.G., Holt, J. (2006). The effects of habitat on dispersal patterns of an invasive thistle, Cynara cardunculus. Biological Invasions, 577-593.
This study quantifies and compares C. cardunculus dispersal patterns in a vegetated field and a non-vegetated field.
Potts, D.L., Harpole, S., Goulden, M. (2008). The impact of invasion and subsequent removal of an exotic thistle, Cynara cardunculus, on CO2 and H2O vapor exchange in a coastal California grassland. Biological Invasions, 10:1073-1084.
Virdis, A., Motzo, R., & Giunta, F. (2009). Key phenological events in globe artichoke (Cynara cardunculus var. scolymus) development. Annals of Applied Biology, 419-429.
This study compared maximum net CO2 exchange of C. cardunculus when it was present and when it was absent.
White, V.A., Holt, J.S. (2005). Competition of artichoke thistle (Cynara cardunculus) with native and exotic grassland species. BioOne, 53(8):826-833.
White and associates composed a competition experiment that determined early season management to delay artichoke thistle would be an effective control.