Arctotheca calendula (capeweed)

Arctotheca calendula has the potential to infest turf and pasture and can compete with economically important crops. It can cause allergies and dermatitis in sensitive individuals and also negatively affects stock production.

A. calendula was first identified in the USA in 200,1 in California, and was added to the US Federal Noxious Weed List and seed list in 2010.

A. calendula is a rosette-forming perennial usually infesting disturbed, urban, and coastal habitats. It prefers a good amount of sun and sandy, well-drained soil. It can grow up to 25 centimeters tall (10 inches) and exhibits purple or yellow daisy-like flowers that can reach 6 centimeters (2.5 inches) in diameter. The plant is pollinated primarily by butterflies. A sterile, vegetatively reproducing yellow-flowered race is not currently regulated in California, but is noted by some to escape from cultivation. This form is now considered a separate species, A. prostrata, sometimes sold in the nursery trade. The invasive A. calendula is regulated in California has purple-tinged disc flowers, is seed-producing, and listed as a category A weed.

A. calendula was first identified in 2001, when USDA APHIS Plant Protection and Quarantine officers detected A. calendula achenes in oats imported from Australia as livestock feed. The plant currently can be found in the coastal prairies in the San Francisco Bay area and on California’s north coast.

A pest risk assessment completed by APHIS, USA (Lehtonen, 2003) ranked A. calendula high for both consequences of introduction and likelihood of introduction, resulting in a ranking of high overall risk potential and the species was added to the US Federal Noxious Weed List and seed list in 2010.

Cal-IPC. Arctotheca calendula (sterile/fertile capeweed). California Invasive Plant Council. Accessed 15 June 2009. http://www.cal-ipc.orgLehtonen

Lehtonen, Polly. 2003. Weed Risk Assessment for Arctotheca calendula (L.) Levyns (cape weed) Version 6. Revised February 2009 by Shirley Wager-Pagé. http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/riskassessments.shtml