Flora of North America species comparison

Subspecies 4 (4 in the flora).

Artemisia tridentata has undergone considerable taxonomic revision in the past century and circumscription of subspecies remains a topic of considerable controversy. Workers in the field should be aware of the morphologic variation within the subspecies across the range of the species (i.e., approximately from the Sierra Nevada in the west to the plains of the Rocky Mountains in the east). Because rangeland managers and conservationists can often identify local morphologic and chemical races based on grazing or habitat preferences of wildlife and domestic animals, some impetus exists to further subdivide the subspecies within A. tridentata at the varietal level. This treatment of the species complex remains conservative in light of the need for further study. As to chemical differences among the subspecies, aroma is often used to distinguish subspecies in the field. Volatile resins in the plants are strongly aromatic and, when crushed, leaves have very distinctive (although not easily described) aromas.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

species ca. 350–500 (50 in the flora)

As circumscribed here, there are five subgenera in Artemisia; four are represented in the flora area.

Etymologies of the common names used for Artemisia species provide glimpses of their uses and demonstrate the rich diversity within the genus. The common name ‘mugwort’ is from the Old English mucgwyrt, mucg meaning ‘midge,’ and refers to the use of Old World herbaceous species in repelling flies and midges. Artemisia was called Motherwort in nineteenth century Maine (as an indication of the high esteem for this otherwise rather pedestrian plant), and in the herbal by R. Banckes (1525): “This herb helpeth a woman to conceyve a chylde, and clenseth the mother, and maketh a woman to have her flowers.” Early settlers in North America brought European plants of A. dracunculus, A. vulgaris, A. absinthium, and A. abrotanum into their herb gardens for seasoning and medicinal uses; they would also have learned about aboriginal uses of Artemisia species native to North America, uses that included fertility rites (sagebrush in western North America) and antihelminthics (wormwoods of grasslands and mountain habitats). Immigrants used A. annua (sweet Annie) in potpourris and later recognized its utility as an anti-malarial drug, a use that was well known in oriental medicine. ‘Bulwand’ is the local name used for herbaceous wormwoods in Scotland, and ‘green-ginger’ and ‘Sailor’s tobacco’ are local names in England (T. Coffey 1993). Use of the names ‘sagewort’ and ‘sagebrush’ in North America arise from the familiar aroma of culinary sage, Salvia officinalis (Lamiaceae). Because true sages (Salvia) and sagewort/sagebrushes (Artemisia) are in separate families, the chemical similarities are an example of convergent evolution. The intense aroma and bitter taste of the plants from terpenoids and sesquiterpene lactones discourages herbivory and undoubtedly has contributed to the remarkable evolutionary success (measured by abundance as well as diversity) of species in this genus.

Members of Artemisia are wind-pollinated and their heads and florets are exceptionally small (even for composites) and, consequently, difficult to examine and assess. Nevertheless, the sexual constitution of floral heads is important in recognition of subgenera. Plant habits and ornamentations of receptacles have also figured in arriving at subgeneric circumscriptions; additional characteristics are enumerated in the descriptions.

Artemisia has a well-deserved reputation for being taxonomically difficult. The number of subgenera varies from four to five in modern treatments, and the number of taxa recognized at the species or subspecific levels varies between 250 and 500 (K. Bremer and C. J. Humphries 1993; H. M. Hall and F. E. Clements 1923; Y. R. Ling 1982, 1995; P. P. Poljakov 1961; M. Torrell et al. 1999). In this treatment, I recognize four native subgenera; subg. Seriphidium is endemic to Asia. In the flora area, the greatest diversity occurs in subg. Artemisia. Subgenus Absinthium can be segregated on the basis of hairs on the receptacle; it may be not phylogenetically distinct (L. E. Watson et al. 2002; J. Valles and E. D. McArthur 2001). Subgenus Dracunculus is clearly distinguished by molecular differences, and subg. Tridentatae is well defined with the exception of A. pygmaea.

This treatment is based on extensive fieldwork, review of recent research, and examination of thousands of specimens; taxonomic circumscriptions remain controversial. Molecular analyses have helped define subgenera but have not clarified relationships between closely related species. The morphologic characters useful in distinguishing species tend to be variable and are often hard to assess (i.e., the sexuality of microscopic florets). Users of the keys will meet with frustrations; descriptions of subgenera and illustrations will help in defining the major groupings of species.

The subgenera are arranged in approximate phylogenetic order; species are arranged alphabetically within the subgenera. Molecular studies define subg. Dracunculus as a major clade that is ancestral to the majority of Artemisia. The subgenera Absinthium, Tridentatae, and Artemisia can be classified as clades; they are weakly supported by molecular evidence.

(Discussion copyrighted by Flora of North America; reprinted with permission.)