This perennial herb has a thick, erect stem that often grows 1.5 meters tall or more, sometimes approaching 2 meters. It has a stout rhizome and can spread to form a colony. The leaf blades have winged petioles and may sheath the stem at the bases. The largest, near the base of the plant, are up to about 15 centimeters long. Those higher on the stem are smaller. The lower leaves may have toothed edges. The inflorescence is usually a large, branching array of many flower heads of varying size. There are 16 to 50 ray floretsper head, each measuring 3 to 14 millimeters long, in shades of blue, pink, or white. The disc florets bloom yellow and turn purple.
Taxonomy
This species may be divided into two subspecies and five varieties:
* S. lanceolatum var. latifolium - eastern Canada and eastern United States
* S. lanceolatum var. lanceolatum - eastern and central Canada and United States, also introduced to Europe
The hybrid of this species with Symphyotrichum novi-belgii, known as Sympyotrichum ×salignum, originates in cultivation but is now naturalised in Europe. Hybrids have also been reported with S. boreale, S. laeve, S. lateriflorum, S. puniceum and S. racemosum. Symphyotrichum lanceolatum was formerly included in the large genus Aster as Aster lanceolatus. However, this broad circumscription of Aster is polyphyletic and the North American asters are now mostly classified in Symphyotrichum and several other genera.
Distribution and Habitat
Symphyotrichum lanceolatum is native to much of Canada excepting the far north, to most of the United States, and to northwestern Mexico in Baja California, Sonora and Chihuahua. The species has been introduced and naturalised in many parts of Europe, from Belgium to Serbia to Latvia. In its native range, Symphyotrichum lanceolatum occurs in a wide variety of mostly moist, open habitats, including riparian areas, meadows and ditches. As an introduced species in Europe, it occurs in disturbed man-made habitats, as well as in riparian areas as an invasive species.
Ecology
In addition to dispersal by wind-blown seed, Symphyotrichum lanceolatum spreads extensively by rhizomes to create large clones. Although these clones do not dominate habitats in North America, growing in association with grasses, goldenrods and other asters, in Europe it is an invasive species that excludes native plants in riparian habitats. This invasiveness has been linked to allelopathic compounds in S. lanceolatum tissue, and their effect on native European plants. Viable seed production in Europe seems to be limited, and the species largely spreads there via rhizomes. The species is visited by a wide variety of pollinatinginsects, including bees, flies, moths and wasps. Cross-fertilisation is usually required to produce viable seed, and as such large clones may have low seed production. Several gall midge species are known to form galls on S. lanceolatum, including Rhopalomyia asteriflorae and Asteromyia paniculata. Leaf-mining insects known to feed on this species include Anoplitis inaequalis, Agromyza curvipalpis, Phytomyza albiceps, Microrphopala xerene, and Sumitrosis inaequalis. Younger instars of Gorgone Checkerspot caterpillars will feed on Symphyotrichum lanceolatum.
