Echinacea: The genus Echinacea

4 Echinacea: The genus Echinacea
HISTORICAL TAXONOMY AND NOMENCLATURE
The name Echinacea is applied to an entire genus, classified within the Asteraceae (or composite
family), one of the largest families of flowering plants (Hitchcock and Cronquist, 1973). European
explorers in the 18th century described and named the first species in this genus, Rudbeckia purpurea
L. (Linnaeus, 1753) from the forests of southeastern North America. At the level of the entire
genus, the historical use of Rudbeckia, Echinacea Moench (1794), and a third name, Brauneria
Necker (1790), for the same taxon were recently explained at length (Binns et al., 2001b, 2002a).
In 1818, Thomas Nuttall was the first to distinguish two different groups in the taxon, but he
found them sufficiently similar so as to be varieties and not separate species. Nuttall named his
newly found variety Rudbeckia purpurea var. serotina (Nuttall, 1818). This same variety was
elevated to species Echinacea serotina (Nutt.) DC. by Candolle (1836), who described a total of
four species in the genus Echinacea. We recently discovered a discrepancy between the current
use of the name Echinacea purpurea (L.) Moench and the Linnaean type specimen. In short, the
type specimen designated by McGregor (1968) for the taxon E. purpurea (L.) Moench did not
match the original description by Linnaeus (1753), but it did match Candolle’s description and type
with the name E. serotina (Nutt.) DC. This error apparently occurred when Boynton and Beadle
(in Small, 1903) mistakenly applied the species name Brauneria purpurea to what should have
been called Echinacea serotina (their error was in the species epithet, not the use of the genus
name Brauneria, which was later invalidated). As a result of their misinterpretation of earlier
taxonomies and the error noted above, Boynton and Beadle considered the true E. purpurea (L.)
Moench (by Linnaeus and Candolle) to be a new species, and they gave it a new name, Brauneria
laevigata. Blake adopted this taxon in 1929 with the name Echinacea laevigata (Boynton & Beadle)
Blake. We have proposed the conservation of the names in current use to avoid confusion in the
horticultural and pharmaceutical trade (Binns et al., 2001a, 2001b). A summary of historical events
pertaining to nomenclatural confusion with respect to the two taxa, called “E. purpurea” and “E.
laevigata” today is found in Table 1.1.
Over the course of nearly 2 centuries, taxonomists recorded names and descriptions of a number
of infrageneric taxa in the genus Echinacea in the floristic literature of North America. However,
especially since most publications treated only various parts of the entire geographical range for
Echinacea, they differed in the number of taxa (from 2 to 11 different groups) in various nomenclatural
combinations of species and varieties (Binns, 2001). Cronquist (1945) described four
species (and one variety) in a thorough taxonomic treatment, which was based on type specimens
and herbarium collections. Finally, in 1968, McGregor made a significant contribution to our
understanding of the genus. He sampled many wild populations and performed garden experiments
for 15 years before he published his taxonomy of the genus Echinacea, the first treatment to cover
the entire reported geographical range. McGregor (1968) recognized nine species and four varieties
using morphological traits and chromosome numbers. His findings were limited by the methodology
of the time and he proposed that there may be extensive genetic variation within certain wild
populations of a single species or variety, and that further genetic studies were necessary. Recent
hypotheses indicate that active speciation and evolution within the genus is most likely occurring
in the Ozark Mountains of Missouri and Arkansas, extending into southeastern Oklahoma (Binns
et al., 2002a; McKeown, 1999). This region of the Great Plains is the center of Echinacea diversity.
Morphologically, there is such variability within populations that users of McGregor’s identification
keys have struggled to definitively identify wild and cultivated Echinacea plant materials.
For example, E. pallida (Nutt.) Nutt. var. pallida [E. pallida (Nutt.) Nutt.] has long been cultivated
in Germany, but it was being sold as E. pallida (Nutt.) Nutt. var. angustifolia (DC.) Cronq. [E.
angustifolia DC. var. angustifolia] until identification by phytochemical methods was refined in
the early 1990s (Bauer and Wagner, 1991). (Taxonomic names are those from the revision [Binns
et al., 2002a]. At first reference, each name is followed by square brackets with the synonym
according to McGregor [1968], which is currently the one in commercial use. Revised nomenclature
is used in the figures and tables.) Despite these chemotaxonomic markers for the commercial
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