Systematics of Osmorhiza Raf. (Apiaceae: Apioideae)

Lowry, Porter; Jones, Almut

The genus Osmorhiza comprises ten species and two subspecies of woodland umbellifers native to temperate Asia and the Americas. Quantitative evaluation of nine morphological characters supports the recognition of two distinct subgenera: Glycosma, with a single species, O. occidentalis, and Osmorhiza, with the remaining nine species. The typical subgenus is further divided into three sections, each with three species. A complete synonymy and detailed description is provided for each taxon, along with an analytical key to the subgenera, sections, species, and subspecies. Phytogeographic data indicate that western North America is the center of distribution and diversity, and possibly the center of origin for Osmorhiza, although members of the genus are found in eastern North America as well as Asia and Central and South America. The amphitropical disjunctions between North and South America observed in the ranges of O. chilensis and O. depauperata (both sect. Nudae) are most likely the result of long-distance dispersal by migratory birds. By contrast, the disjunct populations of these taxa that occur in the Great Lakes region and eastern North America probably represent remnants of a more widespread, pre-Pleistocene distribution. The three species comprising Osmorhiza sect. Osmorhiza (the North American O. claytonii and O. longistylis, and the Asian O. aristata) provide an example of the classical eastern North American-eastern Asian pattern of disjunction. Although these taxa are very similar morphologically, the populations probably represent members of a relatively stable floristic assemblage that has persisted in these areas for a long period; the possibility that there has been any recent contact between these disjunct taxa through Beringia seems remote. The members of Osmorhiza sect. Mexicanae (O. brachypoda, O. mexicana, and O. glabrata) exhibit a somewhat broken distribution from northern California to central Argentina, and possibly represent derivatives of a common ancestral taxon that migrated southward along a chain of mountain tops with suitable temperate climatic conditions at some time during the Pliocene or Pleistocene. Ethnobotanical evidence indicates that at least five species of Osmorhiza were used for medicinal purposes by native Indian peoples of North America. The roots and greens of two species were also consumed as food by both North and South American Indians.

Systematics of Osmorhiza Raf. (Apiaceae: Apioideae)

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