ABSTRACT
The genus Cirsium (Compositae) contains around 120 species distributed across Europe, North Africa, West and North Asia, and North and Central America. The genus Cirsium is closely related to the genus Carduus from which it can be morphologically distinguished by the feathered pappus of the achenes. It contains annual, monocarpic perennial, and polycarpic perennial species. Many Cirsium species (but probably not C. vulgare (Savi) Ten.) are sexually dimorphic. This has been especially well documented for C. arvense (L.) Scop. 4 , 14 , 18 and C. palustre (L.) Scop. 4 The economic value of the genus is very limited. Some species, for instance C. arvense and C. vulgare, are notorious, troublesome weeds in agriculture. C. arvense 24 and C. palustre 2 have been suspected of negative (allelopathic) effects on surrounding vegetation (but see Reference 5). Sometimes Cirsium species (e.g., C. congestum Fisch. et Mey., C. spectabile DC, C. ciliatum Moench, and C. altissimum Hill.) are used as ornamental plants in gardens, 13 or as a summer-cut flower (C. japonicum DC). Symbolically, the spinous Cirsium species stand for power. For zoologists, Cirsium (and Carduus) species are especially interesting because the flowering stem and the flow-erheads provide a habitat for a wide variety of animal species. 23 , 28 An excellent review of the insects feeding on C. vulgare and C. arvense is given by Redfern’s field-guide Insects and Thistles. 23 Some of the insects that feed on the floral parts of the plants are often used in the biological control of thistles. 12
