Cynara cardunculus

Family: Asteraceae

Common names: Artichoke Thistle, cardoon

• Description

Artichoke thistle (Cynara cardunculus) is a spiny thistle of the sunflower family, head high, occasionally taller, crowned by a cluster of showy, bright purple thistle flowerheads that are two to three inches in diameter from April through July. Rarely, patches of white-flowering plants are found (Munz 1963, Kelly pers. observation). One to several stout flower stalks rise from a bushy rosette up to five feet in diameter. A spray of basal leaves, each deeply lobed and gray-green, to four feet in length, arches gracefully up and out from the base. Smaller leaves, otherwise similar in appearance, grow from the flower stalk as it extends upwards. Stout spines on the leaves, stems, and bracts around the flowerheads make it easy to recognize.

• Location

Native around the Mediterranean region.  Artichoke thistle is found in disturbed places, to 1,650 feet (<500 m), throughout the state, except deserts (Hickman 1993). It is common in annual rangelands, especially with a coastal influence, but also is found inland in disturbed grasslands or abandoned agricultural fields and is associated with overgrazing (Thomsen et al. 1986). It was one of the worst pests on California rangelands by the 1930s, invading over 150,000 acres in thirty-one counties and requiring prodigious and expensive efforts to eradicate or control it. By the 1980s the worst concentrations of the plant were found in Orange, Solano, and Contra Costa counties, with locally dense populations elsewhere in the Coast Ranges, Central Valley, and Sierra Nevada foothills (Barbe 1990). Placement on the California Department of Food and Agricultures B List reflects the fact that it became too widespread and difficult to eradicate in many areas, with the authorities opting for preventing its spread, and control when feasible.

• Culture

Artichoke thistle is an important rangeland problem because it reduces forage production and limits movement of livestock (Thomsen et al. 1986). The stout, upright yet spreading nature of the plant, its formidable spines, and high densities make wildlife movement through it difficult. The arching leaves shade a considerable area. Combined with its aggressive root system, artichoke thistle outcompetes native vegetation for light, water, and nutrients. At high densities it becomes a monoculture that excludes shrubs, herbaceous plants, and even annual grasses. For example, mature broom baccharis (Baccharis sarothroides) declines in vigor when in close proximity to artichoke thistle. The thistle also is a threat to the endangered San Diego thornmint. Artichoke thistle flowers as early as April in southern California and into July throughout its range. In a year of average rainfall in San Diego of nine inches (22.5 cm), a mature plant can produce more than a dozen flowerheads with as many as 200 seeds per head (Kelly 1996). In drier years most established plants sprout, flower, and produce seed, but these plants are usually smaller than plants growing during wetter years. Some established plants will sprout and then wither before flowering.

• Usage

As mentioned, dry aerial biomass of cardoon can be used as raw material for fuel usage in large scale combustion plants, either for electricity production or for heating applications. The whole average values of gross heat power and low heat power are respectively 4,000 and 3,714 kcal/kg (16,744 and 15,547 KJ/kg) of dry biomass.

• Features

Artichoke thistle flowers as early as April in southern California and into July throughout its range. In a year of average rainfall in San Diego of nine inches (22.5 cm), a mature plant can produce more than a dozen flowerheads with as many as 200 seeds per head (Kelly 1996). In drier years most established plants sprout, flower, and produce seed, but these plants are usually smaller than plants growing during wetter years. Some established plants will sprout and then wither before flowering. Because of artichoke thistles ability to resprout after chemical spraying and to build up a seedbank that lasts five years or more, yearly monitoring and repeat eradication are necessary. Eradication is most effective when mature plants are bolting, generally in early to mid-April in southern California and late April or May farther north. Chemical control efforts have proved successful on sizable populations in several open-space parks and on military lands managed for their natural resources in San Diego County. Seedbanks in some areas have been exhausted, and maintenance is minimal and routine (Kelly pers. observation).

• References

USDA Plants Database

Biomat.net

UC Cooperative Extension

Arundo donax Cynara cardunculus Tamarix ramosissima

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