Centaurea stoebe subsp. micranthos
From BugwoodWiki
Authors: Carey Minteer, University of Georgia
|
Contents |
The plant
Photo by Marisa Williams, University of Arkansas, Fayetteville, Bugwood.org
Centaurea stoebe subsp. micranthos (Spotted Knapweed; syn. C. maculosa auct. non Lam.) is a distinctive member of the Asteraceae with pink/purple flowers and black-tipped phyllaries. The mid-stem leaves are pinnately lobed to pinnately compound, as leaves move up the stem they become less dissected and much smaller. It is a diploid or tetraploid short-lived perennial that can live up to nine years (Boggs and Story, 1987).
Photo by Norman E. Rees, USDA Agricultural Research Service, Bugwood.org
Distribution
Spotted knapweed is a native of Europe and western Asia with its distribution from central and southeast Europe, northern Italy, and central Russia (Tutin et. al., 1976).
Introduction to North America
It was accidentally introduced into North America in 1890s in alfalfa seed from Asia Minor (Mauer et al., 1987). The seeds of spotted knapweed were also believed to be released into port in Victoria British Columbia in 1893 as contaminate in ship ballast. Spotted knapweed was first collected in Victoria British Columbia in 1893 (Groh, 1944). Spotted knapweed began to spread rapidly about 50 years ago (Eddleman & Romo, 1988). It has now spread into 45 of the 50 U.S. states and is found in Canada from Nova Scotia to British Columbia. It is listed as a noxious weed in 13 states (USDA, 2005). Spotted knapweed has been a serious invader of rangelands in the Rocky Mountain region and has invaded 1.9 million ha (4.7 million acres) in Montana alone (Alpher, J., 2004).
Habitat
The plants prefer high sun exposure, but a preference for a specific soil type has not been found (Ochsmann, 2001). Spotted knapweed is most often found on disturbed sites such as roads; however, in the Pacific Northwest it is known to invade pastures where it causes the overgrazing of native grasses (Lacey et al., 1990; Tyser and Key, 1988). Watson and Renny (1974) found that level of disturbance was positively correlated to knapweed density.
Invasiveness
Spotted knapweed reproduces mostly by seed but may spread by some lateral root sprouting that produces new rosettes (Watson and Renney, 1974). Plants produce on average 1,000 seeds per plant or anywhere from 5,000-40,000 seeds/m² (Sheley et al., 1998). The seeds are dispersed by vehicles and hay that is transported by farm equipment. Seeds are also dispersed by wind and animals. Jensen and Six (2006) have shown that the elaiosomes on the seeds of spotted knapweed may increase dispersal by ants. Upon maturation the seeds remain viable for eight years (Davis et al., 1993). Spotted knapweed’s invasive behavior is also increased by the allelopathic chemical (-)- catechin. This chemical is secreted by the roots of spotted knapweed and has been shown to suppress germination and root and shoot differentiation of some grasses and row crops such as wheat (Bais et al., 2002). It has been shown in vitro that spotted knapweed begins to secrete lethal levels of (-)- catechin within 2-3 weeks of germination (Weir et al., 2003).
References
- Alpher, J. (2004). Wicked weed of the west. Smithsonian. 2005.
- Bais, H. P., Walker, T. S., Stermitz, F. R., Hufbauer, R. A., and Vivanco, J. M. (2002). Enantiomeric-dependent phtotoxic and antimicrobial activity of (+/-) catechin. A rhizosecreted racemix mixture from spotted knapweed. Plant Physiology. 128:1173-1179.
- Boggs, K. W., and Story, J. M. (1987). The population age structure of spotted knapweed (Centaurea maculosa) in Montana. Weed Science. 35:194-198.
- Davis, E. S., Fay, P. K., Chicoine, T. K., and Lacey, C. A. (1993). Persistence of spotted knapweed (Centaurea maculosa) seed in soil. Weed Science. 41:57-61.
- Eddleman, L. E., and Romo, J. T. (1988). Spotted knapweed germination response to stratification, temperature, and water stress. Canadian Journal of Botany. 66:653-657.
- Groh, H. (1944). Canadian weed survey. 2nd annual report. Ottawa, ON.
- Jensen, J. M., and Six, D. L. (2006). Myrmecochory of the exotic plant, Centaurea maculosa; A potential mechanism enhancing invasiveness. Environmental Entomology. 35(2): 326-331.
- Lacey, J., Husby, P., and Handl, G. (1990). Observations on spotted knapweed and diffuse knapweed invasion into ungrazed bunchgrass communities in western Montana. Rangelands. 12: 30-32.
- Ochsmann, J. (2001). On the taxonomy of spotted knapweed (Centaurea stoebe L.). Proceedings from The First International Knapweed Symposium of the Twenty-First Century. March 15-16, 2001. Coer d' Alene, Idaho. 33-41.
- Sheley, R. L., Jacobs, J. S., and Carpinelli, M. F. (1998). Distribution, biology, and management of diffuse (Centaurea diffusa) and spotted knapweed (Centaurea maculosa). Weed Technology. 12: 353-362.
- Tutin, T. G., Heywood, N. A., Burges, D. M., Moore, D. M., Valentine, D. H., and Walters, S. M. (1976). In Webb D. A. (Ed.), Flora Europea 4. Plantaginaceae to Compositae (and Rubiaceae). Cambridge. Cambridge University Press.
- Tyser, R. W., and Key, C. H. (1988). Spotted knapweed in natural area fescue grasslands: An ecological assessment. Northwest Science. 62(4):151-159.
- United States Department of Agriculture. (2007). Plants Database. Centaurea stoebe subsp. micranthos. Retrieved 8/15, 2007, from http://plants.usda.gov/java/profile?symbol=CESTM
- Watson, A. K., and Renney, A. J. (1974). The biology of Canadian weeds. Centaurea diffusa and C. maculosa. Canadian Journal of Plant Science. 54: 687-701.
- Weir, T. L., Bais, H. P., and Vivanco, J. M. (2003). Intraspecific and interspecific interactions mediated by a phytotoxin, (-) catechin, secreated by the roots of Centaurea maculosa (spotted knapweed). Journal of Chemical Ecology. 29(11): 2397-2410.
Cminteer 16:35, 23 January 2008 (EST)
