A morphometric analysis was conducted of Echinacea Moench (Asteraceae) to measure variation between native populations for taxonomic purposes. Data were collected from living and herbarium specimens. From a matrix of 321 specimens by 74 characters, a pair-wise distance matrix was computed using Gower's coefficient. Cluster strategies were explored from the distance matrix. MODECLUS clustering separated the data into two clusters, and a flexible agglomerative clustering method separated the data into the same two clusters, which were broken into four sub-clusters. Canonical discriminant analysis gave significant support for the two- and the four-cluster solutions. Canonical discriminant analysis also showed support for eight smaller clusters identified using McGregor's 1968 classification. We recognize two subgenera and four species: Echinacea subg. Echinacea contains only E. purpurea; Echinacea subg. Pallida contains E. atrorubens, E. laevigata, and E. pallida. The revised varieties are as follows: E. atrorubens var. atrorubens, E. atrorubens var. neglecta, E. atrorubens var. paradoxa, E. pallida var. angustifolia, E. pallida var. pallida, E. pallida var. sanguinea, E. pallida var. simulata, and E. pallida var. tennesseensis. A cladistic analysis was done on the four species. In the most parsimonious solution, E. purpurea was basally divergent to a clade of the other three species (70% bootstrap value), and all four were distinguishable by at least one apomorphy. A key to Echinacea taxa is provided, which should be valuable given the pharmaceutical and horticultural importance of Echinacea.
Communicating Editor: Paul Wilson