Artemisia Linnaeus, 1753

Grown as a medicinal plant, most commonly as a vermifuge, Artemisia vulgaris is widely established in eastern North America and is often weedy in disturbed sites. Populational differences in morphologic forms are reflected in size of flowering heads, degree of dissection of leaves, and overall color of plants (from pale to dark green), suggesting multiple introductions that may date back to the first visits by Europeans. It is tempting to recognize the different forms as subspecies and varieties; the array of variation in the field is bewildering. If genetically distinct forms exist in native populations, the differences appear to have been blurred by introgression among the various introductions in North America. A case could be made for recognizing var. kamtschatica in Alaska based on its larger heads and shorter growth form; apparent introgression with populations that extend across Canada confounds that taxonomic segregation.

A. superba Pamp. in Nuov. Giorn. Bot. Ital. n. s. 36: 473. 1930.

Mugwort is one of the introduced Artemisia spp. and rather nondescript in appearance. While significantly lobed, its leaves are usually broader than other Artemisia spp. and more tolerant of shade. These leaves are bicolored

This introduced perennial plant is 2-4' tall, branching abundantly in the upper half where the flowerheads occur. The stems are largely hairless, angular, and furrowed, although the upper flowering stems are usually pubescent. The lower stems often become reddish or woody in appearance with maturity. The alternate leaves are up to 4" long and 3" across, becoming smaller in size and more narrow as they ascend the stems. The upper surface of these leaves is green and hairless, while their lower surface is white from fine pubescent hairs. The lower and middle leaves usually have 1-2 pairs of deep primary lobes that are often irregularly spaced; these primary lobes are often shallowly cleft by one or more secondary lobes, or they have may a few large teeth. At the base of these leaves, there are often 1 or 2 small eared lobes. The upper leaves have few lobes or none, eventually becoming linear on the flowering stems. The inflorescence is a large panicle of leafy spikes with flowerheads. Each flowerhead is 1/8" across or a little larger, consisting of numerous rayless florets. The florets in the center of the flowerhead are fertile and perfect, while the florets along the outer margin of the flowerhead are fertile and pistillate. The central florets are tubular with 5 recurved lobes, while the marginal florets have only 1 or 2 lobes. All of these florets have a divided style. At the base of the flowerhead are several floral bracts that are finely pubescent. Except for their abundance, these flowerheads are inconspicuous. At the bud stage they are whitish green, becoming dull yellowish green or purplish green with maturity. The blooming period occurs from late summer to early fall, and lasts about 1-2 months. Pollination is by wind. Each floret is replaced by an oblong achene that is without a tuft of hairs. These achenes are small and light enough to be blown about by the wind. The root system is quite rhizomatous, and often produces vegetative colonies of plants.