A Review of the Taxonomy of the Genus Echinacea

Echinacea (Asteraceae), a North American genus of 11 recognized taxa (McGregor 1968), is of great economic and scientific interest. Three species, E. angustifolia DC. var. angustifolia, E. pallida (Nutt.) and E. purpurea (L.) Moench, show potential pharmacological activity (Bauer et al. 1988a; Bauer and Wagner 1991). Hydroalcoholic extracts of the roots of these three taxa stimulate phagocytosis in vitro, but there are no conclusive human clinical trials to date that fully substantiate the immune stimulating effects of such extracts upon oral administration. Although these taxa have been subjected to extensive chemical characterization (Bauer et al. 1988b; Bauer and Remiger 1989; Bauer et al. 1988, 1989), the exact chemical identity of the active constituents is unknown (Awang 1999). There is historical documentation of the medicinal uses of Echinacea by the North American Plains Indians (Kindscher 1989). This ethnobotanical validation has certainly been a factor in the popular herbal use of Echinacea, which has skyrocketed over the last few decades. The market demand and the medicinal properties are responsible for the recent interest in this genus as a new specialty crop. All species of Echinacea are herbaceous, perennial flowering plants of the composite family (Asteraceae). Generally, a basal rosette of petiolate leaves and one to several annual stems arise from an underground, perennial rootstock. A single taproot is characteristic of all species except for E. purpurea, which has a fibrous root system. The stems terminate in a long-lasting and mildly fragrant inflorescence. The disk flowers are attached to a conical, hemispherical or occasionally flattened receptacle. The disk itself may also be flattened, conical, or hemispheric. Surrounding the capitulum is an involucre of 3 to 4 series of imbricating bracts (phyllaries). Each disk floret is subtended abaxially by a modified bract, the palea, which protrudes beyond the 5-lobed corolla. The disk florets are protandrous and development and anthesis follow the typical centripetal pattern of development of the composite family. The whorls of sharply tipped palea give a distinctive look to the capitulum; indeed, the genus name is derived from the Greek word echinos, for hedgehog. Pubescence on the stems, leaves and bracts ranges from hispid, hirsute and strigose to glabrous and varies among the species. The sterile ray flowers have strap-shaped ligules with colors that range from white, pink, magenta and purple to yellow. The majority of taxa are diploid (n = 11). E. pallida and some populations of E. angustifolia var. strigosa McGregor are tetraploid (n = 22) (McGregor 1968). A complete understanding of the reproductive biology and breeding system is lacking; the presumed sporophytic self-incompatibility system is not perfected in this genus. Every species of Echinacea self pollinates to some degree, E. purpurea more so than the others (McGregor pers. commun. 1997). A mixed breeding system has been recently demonstrated for E. angustifolia var. angustifolia (Leuszler et al. 1996). In addition to its possible medicinal uses, Echinacea has enormous ornamental potential. E. purpurea, the only species for which ornamental cultivars have been bred, is both productive and profitable as a field grown specialty cut flower (Starman et al. 1995). In fact, E. purpurea is the only species of the genus which has been domesticated thus far. It is interesting to note that the cultivars of E. purpurea that are now in production as source materials for herbal extracts were actually developed for ornamental purposes. Com-