ASCLEPIAS VERTICILLATA AND ROADWAYS OF THE UPPER MIDWEST: FROM HOME ON THE RANGE TO LIFE IN THE FAST LANE

摘要

Asclepias verlicillata L. (whorled milkweed) is a native perennial member of the family Asclepiadaceae. Stems (ramets) are usually 20-80 cm tall and bear small white flowers (sometimes with green and/or purple highlights) in umbels. The seed-pods (follicles) are usually 1 cm wide and 6-8 cm long. The leaves are numerous, entire, 2-8 cm. long, 2-5 mm wide, and are produced in whorls. The plant (a genet) grows from a shallow underground rhizome and can bear from one to many above-ground stems. Asclepias verticillata has laticifers that exude sticky white latex when damaged. It is distributed from southern Manitoba, Ontario, Wisconsin, Michigan, New York and Massachusetts, south into Florida and the Gulf States, and west to Montana, Wyoming, Colorado, and New Mexico. Throughout this range it is reported from a diversity of habitats including dry to dry-mesic prairies, savannas, thin woods, roadsides, pastures, rocky cliffs, and old fields (Braun 1989; Gleason and Cronquist 1991; Mohlenbrock 1986; Voss 1996). In June of 1994 I found thousands of flowering stems of A. verticillata in the median of US highway 131, just north of its intersection with Shaver Road in Kalamazoo County, MI. I later found plants to be exceptionally abundant in similar conditions elsewhere in Kalamazoo County. Prior to these discoveries I had thought A. verticillata to be nearly extirpated in the vicinity of Kalamazoo. To determine if A. verticillata occurred along additional highway, and interstate roadsides in the upper Midwest (here defined as Indiana, Illinois, Michigan, and Ohio), I visually surveyed for plants along roadsides in this region over the following 6 summers.