Myriophyllum quitense (Haloragaceae) in the United States

A systematic study of more than 15,000Myriophyllum specimens from 189 North American herbaria yielded 63M. quitense specimens. Late 19th century collections were made from Henry's Fork of the Snake River in Jefferson County, Idaho, in 1872, from Santa Cruz Creek, Tucson, Pima County, Arizona, in 1881, from Yellowstone Lake in 1885, and from Crook County, Oregon, in 1894. Twentieth century collections have been made from Yellowstone National Park, at several sites along the Snake River in Idaho, in Summit County, Utah, in Lassen and Shasta counties of northern California, at numerous sites along the Deschutes River, and in Benton County, Oregon, and at three sites in Washington. We contend that the species was introduced into North America by migratory waterfowl more than 100 years ago. Only in the Yellowstone Lake and numerous Deschutes River habitats in which populations now exist are environmental conditions conducive to full morphological development of the species in North America.