Erigeron decumbens var. decumbens (Willamette daisy)
by
, former President, Native Plant Society of Oregon rglove@uoregon.edu
Willamette daisy is endemic to the Willamette Valley of Oregon and was likely at one time widespread through this region. However, by the end of the 1970s the plant was considered extinct, the last collection having been made in 1934. Fortunately in 1980, two small populations were re-discovered, but then, tragically, in 1986, the largest population known over 6,000 plants--was destroyed by plowing. Today the eighteen remaining populations are scattered in seven Oregon counties, representing perhaps 7,500 total plants. One site near Eugene has a population that varies between 1,000 and 3,000 plants.
Erigeron decumbens is a showy, tall, blue- or pink-flowered perennial that often grows in clumps and can reach nearly five feet in height -- early Willamette Valley pioneers described wildflowers as high as the belly of a horse. Each taprooted individual, with its numerous stems, may bear 20 to 30 heads. On robust plants, these heads may be nearly 4
Willamette daisy requires heavy soils in seasonally wet, open grasslands. The plant is shade-intolerant, an early-successional species which depends on flooding and fire to maintain its open prairie habitat. Its pollinators are
Erigeron decumbens was discovered and collected by the indefatigable and eccentric English-born botanist Thomas Nuttall (1786-1859), on his famous 1834-35 overland trip with John Kirk Townsend to the Columbia River. Nuttall was not always a careful note-taker, thus the exact locations of some of his collections are problematical. In fact he claims to have encountered the daisy in the Rocky Mountains toward Oregon, however, we can be reasonably certain that he found the plant in the Willamette Valley since it has never been known to grow elsewhere. Nuttall published the name, Erigeron decumbens, in 1840; most of his specimens are preserved at Philadelphia, Harvard, and the British Museum. No type specimen has been designated for E. decumbens. Nuttall may have chosen the name decumbens because this tall plant often falls over or becomes decumbent due to prairie winds and rains. Botanists also use this term for plants that have a curved base below upright branches. Nuttall's name remained unchanged for 107 years until 1947, when Arthur Cronquist, the American expert on the sunflower family, wrote a revision of the genus Erigeron. While working with CL Hitchcock on the flora of the Pacific Northwest, Cronquist recognized a California variety of E. decumbens that he named var. robustior. This automatically changed the name of our Willamette daisy to Erigeron decumbens var. decumbens. However, that is not the end of the story, because Guy Nesom, who has written the treatment for Flora of North America, now recognizes E. robustior as a species in its own right. Thus, according to the rules of botany, the name of our daisy once again becomes Erigeron decumbens, restoring Nutall's original 1840 name.
Center for Plant Conservation. Erigeron decumbens var. decumbens.
Chambers, K. 2007. Personal correspondence.
Clark, DL, Ingersoll, CA, Finley, KK, 1997. Regeneration of Erigeron decumbens var. decumbens (Asteraceae), the Willamette Daisy. IN: Kaye TN et al, Conservation and management of native pants and fungi. Native Plant Society of Oregon, Corvallis.
Cronquist, A. 1947. Revision of the North American species of Erigeron. Brittonia 6:121-302.
Dept of Interior, Fish and Wildlife Service. October 2006. Designation of Critical Habitat for three Willamette Valley species.
Federal Register. June 15, 2006, Vol. 71, No. 115. Proposed designation of critical habitat for Erigeron decumbens.
Hitchcock CL, A. Cronquist, M. Ownbey, JW Thompson. 1955. Vascular plants of the Pacific Northwest, Part 5.
McKelvey, SD. 1956. Botanical exploration of the trans-Mississippi west 1790-1850. Harvard University.
Meinke, R. 1982. Threatened and endangered vascular plants of Oregon: an illustrated guide. US Fish and Wildlife Service, Portland.
Nesom, G. 2(2006) Flora of North America treatment of genus Erigeron. Erigeron decumbens Vol. 20, p. 279
Nuttall, T. 1840. Trans. Am. Phil. Soc. 7:309.
Oregon Flora Project. Map: Distribution of Erigeron decumbens (PDF, 806kb, includes photos). OFP, Oregon State University and OSC Herbarium.
Oregon Flora Project. Rare Plants
Oregon Natural Heritage Information Center, 2004. Rare, threatened and endangered plants of Oregon, Oregon State University, Portland. ONHIC web site
Thorpe HS, and TN Kaye 2006. Erigeron decumbens ssp. decumbens (Willamette Daisy) Population monitoring and evaluation of mowing and burning at Oxbow West, West Eugene wetlands, BLM Eugene District and Institute of Applied Ecology. kayet@peak.org