861401 Achillea millefolium L.
- L., Sp. Pl.: 899 (1753). Lectotype (LINN): Europe. Herb. Linn. 1017.20 (Huber-Morath 1974: 154).
Notes: The Achillea millefolium group is at several ploidy levels and complicated morphologically, with little documentation yet of good correlations between ploidy and morphology. The reported morphological differences are small, mainly concerning size features, shape of inflorescence, colour of involucral bracts, and pubescence. Several studies have focused on the variation at local and regional scales (e.g., Lawrence 1947, Mulligan and Bassett 1959, and Gervais 1977 in North America; Briggs et al. 1965 in Europe). We have not found any recent or molecular studies of relevance for the northern plants. Treatments of these differ and no satisfactory solution has been reached.
Five names have been in frequent use, based on plants from widely separated areas: "millefolium" from temperate Europe, "lanulosa" from temperate North America, "apiculata" from the Murman area in northwestern European Russia, "borealis" from southeastern Alaska, and "nigrescens" from Labrador in eastern Canada. Our questions are how many taxa the plants that reach the Arctic should be divided on and what ranks and names they should be assigned.
Several authors accept the temperate plants as two species or races: the Eurasian A. millefolium s. str. (adventive in Greenland and in non-arctic parts of North America) and the North American A. lanulosa (A. millefolium subsp. lanulosa, for Iceland see below). Both reach the Arctic, mostly close to the borderline. The main arctic-alpine race in North America has often been named A. millefolium subsp. borealis (or subsp. nigrescens) and seems to be the same from the Atlantic to the Pacific. In its major features it resembles A. millefolium subsp. lanulosa except for its darker involucral bracts. Russian authors (e.g., Tzvelev 1987e; Korobkov PAF proposal) have divided the arctic Eurasian plants on A. apiculata in northwestern European Russia (and obviously also northern Norway) and A. nigrescens with a strongly disjunct northern range from northeastern European Russia to Chukotka and North America. Hultén (1968a) and Hultén and Fries (1986) accepted three main entities. They assigned all northern Eurasian plants to A. millefolium, whereas they divided the North American material on temperate A. lanulosa and arctic-alpine A. borealis. Cody (1996) chose a solution of subspecies as concerns the North American representatives.
As for recent studies, the study of Guo et al. (2004) did not apply molecular markers appropriate at these low taxonomic levels. Their analysis did not differentiate between samples assigned to A. millefolium s. str., A. millefolium subsp. sudetica, and A. lanulosa. The treatment of Trock (2006a) did not elucidate the matter further. It applied a wide A. millefolium without races for North America, but with some discussion.
We are not convinced that there is much difference between the temperate and the arctic plants or between those in North America and in Eurasia. We have chosen treatment as three subspecies (with nearly all Eurasian plants in one subspecies) in wait for a combined morphological and molecular analysis. One reason for acceptance of races is the situation in Iceland where two rather different entities seem to co-occur.