Plant Genera


Family Code: ASTERA
Genus Code: EUPAT
Genus CN: thoroughwort
Genus Authority: L.
Genus Summary: A genus of about 40 species, herbs, of e. North America and Eurasia (after the exclusion of Ageratina, Chromolaena, Conoclinium, Eutrochium, Fleischmannia, and other genera). I have differed considerably from Cronquist's treatments, as for instance in SE, regarding the rank at which to recognize taxonomic entities in Eupatorium. In the Southeastern United States, Eupatorium is a reticulately evolved complex, including diploids, triploids, and tetraploids; derivatives of hybridization produce sterile pollen but in some cases reproduce vigorously via agamospermous production of seeds. In some cases, these entities form separate populations from their presumed parental species, with distinctive ranges and habitats and more-or-less distinctive morphology. Cronquist treats morphologically highly distinctive entities, such as E. pinnatifidum, as full species, while stating that they are "not long-persistent." He treats morphologically more subtle entities as varieties of one of the two presumed parental species, such as E. album var. vaseyi ("very probably derived by hybridization of E. album var. album and E. sessilifolium"). Other entities, difficult to distinguish morphologically from another species, he does not recognize, as for instance E. saltuense, included as a synonym under E. altissimum ("E. saltuense may reflect hybridization between E. altissimum and some other species such as E. album, or possibly between E. hyssopifolium and E. album"].
Genus References: Siripun & Schilling in FNA (2006c); Schilling (2011)=Y; Cronquist (1980)=SE; Godfrey (1949). The key adapted from those references. (also see Ageratina, Chromolaena, Conoclinium, Eutrochium, Fleischmannia)
Last Updated: 2019-11-29
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