The biology of Canadian weeds. 113. Symphyotrichum lanceolatum (Willd.) Nesom [Aster lanceolatus Willd.] and S. lateriflorum (L.) Löve & Löve [Aster lateriflorus (L.) Britt.]

Abstract

Symphyotrichum lanceolatum, the tall white aster, is a morphologically variable, native North American, polyploid (tetraploid, pentaploid, hexaploid, heptaploid, and octoploid cytotypes) species with a transcontinental distribution. Commonly found along fence rows, ditches, road and rail right-of-ways, and field, pond, and wood lot margins, the species is not a serious agricultural weed but may become problematic in neglected fields, poorly managed pastures, and cultivated fields on recently plowed land. For this review of the biology of the species, we recognize two subspecies, the eastern subsp. lanceolatum and western subsp. hesperium. The former is further divided into varieties lanceolatum, hirsuticaule, interior, and latifolium. Symphyotrichum lateriflorum, the one-sided aster, is also morphologically variable. The distribution of this native, polyploid (diploid, tetraploid, hexaploid, and octoploid cytotypes) extends from the Magdalen Islands and Prince Edward Island in the north, south to Florida, Mississippi, Louisiana, and Texas. Occurring in a variety of habitats, including dry to wet thickets, open woods, shorelines, mesic to wet-mesic prairies, and dry open places, the species is possibly the least weedy of the weedy asters in Canada, but nonetheless may become problematic in neglected fields, poorly managed pastures, or roadside right-of-ways. Although several varieties have been described, little agreement surrounds their recognition, as characters considered useful by some are designated useless by others. This contribution summarizes the known biological data for the two species.