My introduction to the genus Echinacea came as the result of collecting 88 of the 150 accessions now maintained by the U.S. Department of Agriculture's (USDA) Agricultural Research Service for the National Plant Germplasm System of the United States. This germplasm represents a comprehensive sampling of Echinacea diversity and includes all species recognized by McGregor
(1968) in his early taxonomic monograph. As of this writing, the wild seed of 80 Echinacea accessions has been increased in controlled pollination cages and is now available through the Germplasm Resources Information Network (GRIN) at http://www.ars-grin.gov/npgs. During the germplasm cultivation in a common field over several years, morphological characters were evaluated and taxonomic identification per McGregor (1968) was verified; this information is accessible through the GRIN database (Widrlechner and McKeown, 2002). Further evaluation of the germ-plasm is underway, including a root phytochemical analysis of these same 80 accessions in the laboratory of James Simon at Rutgers University.
During the germplasm collection, morphological types that had not been fully characterized from geographic areas of probable hybridization were observed (McGregor, 1968; McKeown, 1999). It is a common misconception that plant hybrids simply display intermediate morphological characteristics (Rieseberg and Carney, 1998). In fact, hybrids reflect varying degrees of parental, intermediate, transgressive, and novel traits, a phenomenon that can compromise the utility of morphological traits in taxonomic identification (Rieseberg and Carney, 1998). However, hybrids do tend to be complementary (additive) in expression of chemical characters, and can also display incomplete complementation, loss of parental compounds, and gain of novel chemistry (Rieseberg and Carney, 1998). Differences in the genetic basis of these two types of traits, quantitative for many morphological characters and single gene for many chemical compounds, can help explain these phenomena (Rieseberg and Ellstrand, 1993). Several USDA accessions now categorized as hybrids in the GRIN database exemplified this type of phenotypic complexity (Widrlechner, 2001). The observation of native hybrids and the documentation of polyploidy (McGregor, 1968) suggest the interesting possibility of hybridization as a speciation process in the genus. Current and evolutionary gene flow among populations and the possible hybrid origin of Echinacea species may become prominent factors in conservation, analyses of diversity, systematics, phylogenetics, and other areas of research, including phytochemistry.
Given the above observations, a few comments should be made on Echinacea systematics. A revision of the McGregor taxonomy (Binns et al., 2002) notwithstanding, I have found McGregor's 1968 classification to clearly distinguish Echinacea species in the greenhouse, phytotron, and field with the exception of the aforementioned natural hybrids. McGregor, who spent 15 years collecting data directly from wild stands of Echinacea, many of which have disappeared (McGregor, 1997), worked in the days prior to the development of phenetics and cladistics and prior to the extensive digging that now characterizes the fragmented and attenuated American prairie. His vast and valuable observations are literally unrepeatable due to wild population loss and decline over the last 35 years. It is unfortunate that taxonomic misunderstanding has arisen (Binns et al., 2002), but this is not attributable to McGregor. Given the power of molecular systematics, the true issue here is whether a morphometric study such as that of Binns et al. (2002) is the appropriate approach for a modern revision of Echinacea classification. The possibility of hybridization as a process in Echinacea speciation and the existence of polyploids will require a molecular systematic investigation of both chloroplast and nuclear genomes to elucidate phylogenetic relationships within the genus. Such a study is now under way in the laboratory of Jonathan Wendel and colleagues at Iowa State University in Ames, Iowa. The morphometric analysis of Binns et al. (2002) will certainly be of value in evaluating concordance between morphological and molecular characters; however, a fully revised systematic classification should also include molecular data. For the time being, therefore, I continue to follow McGregor's taxonomic treatment and will do so in this text.
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