(Map may reflect historical as well as recent sightings)
Nelson's checkermallow was federally listed as threatened without
critical habitat in 1993 (U.S. Fish and Wildlife Service 1993).
A recovery plan was published in 1998 (U.S. Fish and Wildlife
Description and Life
Nelson's checkermallow is a perennial herb in the mallow family
(Malvaceae). It has tall, lavender to deep pink flowers. The flowers
are borne in clusters 50-150 cm (1.6-5 ft) tall at the end of
short stalks. These clusters (inflorescences) are usually spike-like,
elongate, and somewhat open. Plants have either perfect flowers
(male and female) or pistillate flowers (female only). The plant
can reproduce vegetatively, by rhizomes, and by seeds, which drop
near the parent plant. Flowering can occur as early as mid-May
and extend into September in the Willamette Valley, Oregon. Fruits
have been observed as early as mid-June and as late as mid-October.
Coast Range populations generally flower later and produce seed
earlier, probably because of the shorter growing season.
Within the Willamette Valley, Nelson's checkermallow most frequently
occurs in Oregon ash (Fraxinus latifolia) swales and meadows with
wet depressions, or along streams. The species also grows in wetlands
within remnant prairie grasslands. Some populations occur along
roadsides at stream crossings where non-native plants, such as
reed canarygrass (Phalaris arundinacea), blackberry (Rubus spp.),
and Queen Anne's lace (Daucus carota), are also present. Nelson's
checkermallow primarily occurs in open areas with little or no
shade and will not tolerate encroachment of woody species.
In the Willamette Valley, Nelson's checkermallow occurs on soils
in the Wapto, Bashaw and Mcalpin Series (NRCS mapped soil unit
STATSGO 81) and Malabon, Coburg and Salem Series (NRCS mapped
soil unit STATSGO 91).
Reasons for Decline
Prior to European colonization of the Willamette
Valley, naturally occurring fires and fires set by Native Americans
maintained suitable Nelson's checkermallow habitat. Current fire
suppression practices allow succession by introduced and native
trees and shrubs; the trees may gradually invade habitat for Nelson's
checkermallow. Remnant prairie patches in the Willamette Valley
have been modified by livestock grazing, fire suppression, or
agricultural land conversion. Stream channel alterations, such
as straightening, splash dam installation, and rip-rapping cause
accelerated drainage and reduce the amount of water that is diverted
naturally into adjacent meadow areas. As a result, areas that
would support Nelson's checkermallow are lost.
The majority of sites where the species occurs is in the Willamette
Valley of Oregon; the plant is also found at several sites in
the Coast Range of Oregon and at two sites in the Puget Trough
of southwestern Washington. Thus, the range of the plant extends
from southern Benton County, Oregon, north to Cowlitz County,
Washington, and from central Linn County, Oregon, west to the
crest of the Coast Range. The species is known to occur in 62
patches within 5 relict population centers in Oregon, and at 2
sites in Washington.