Interspecific hybridization is known to occur between Nelson’s checkermallow and the other species of Sidalcea that occur within or near its range in the Willamette Valley. However, ecological and genetic barriers appear to limit hybridization among existing populations of these species. Though sexually compatible, Sidalcea nelsoniana flowers later in the year than S. malviflora ssp. virgata in sites where the species co-occur; S. nelsoniana and S. cusickii are fully sexually compatible and share flowering times and pollinators, but their ranges are narrowly separated by less than a mile and the species do not currently co-occur within any known sites; S. nelsoniana and S. campestris co-occur in many sites, but the two species exhibit low sexual compatibility, likely because of chromosomal pairing problems due to differing ploidy levels in the two species.
Nelson’s checkermallow is an erect perennial arising from a stout taproot, the stems 40-100 cm tall and glabrous or with short, simple hairs. Leaf blades are glabrous above and sparsely covered with small, stiff hairs beneath. Basal leaves are round and palmately lobed, the lobes toothed; upper leaves are increasingly deeply cleft. The species is gynodioecious, with plants that are either pistillate (female, lacking stamens) or perfect (having both male and female parts). Racemes are somewhat spikelike, but elongate and open, bearing many flowers. Petals are pinkish lavender, calyces usually purplish tinged. Petals of perfect flowers are 9-15 mm long, the calyx 4.5-7 mm long; petals of pistillate flowers are 5-9 mm long, the calyx 4-6 mm long. Carpels are approximately 3 mm long and lightly reticulate on the sides, the beak less than 0.5 mm long.
Four other Sidalcea species occur within or near the range of Nelson’s checkermallow: S. campestris, S. cusickii, S. hirtipes, and S. malviflora ssp. virgata. Sidalcea campestris is distinguished from Nelson’s checkermallow by its typically taller stature (0.5-2 m tall versus 0.4-1 m tall) and by its petals, which are white to pink (versus pinkish lavender) and usually longer (petals of perfect flowers 13-25 mm long versus 9-15 mm long, petals of pistillate flowers 9-12 mm long versus 5-9 mm long). Sidalcea cusickii occurs just south of the range of Nelson’s checkermallow and has forked to stellate stem hairs (versus glabrous or with simple hairs) and calyx lobes that are broadened above the base and prominently veined (versus calyx lobes not broadened above the base nor prominently veined). Sidalcea hirtipes has stems copiously covered with long hairs (versus stems glabrous or with short hairs) and longer calyces copiously long-hairy (calyces 9-15 mm long with hairs up to 2.5 mm long versus calyces 5-7 mm long and subglabrous to covered with tiny star-shaped hairs). Sidalcea malviflora ssp. virgata usually begins flowering earlier and tends to inhabit dryer, more upland sites, and has stems with forked or branched stem hairs (versus glabrous or with simple hairs) and petals that are deep pink to rose colored (versus pinkish lavender) and typically longer (petals of perfect flowers 15-25 mm long versus 9-15 mm, petals of pistillate flowers 9-13 mm long versus 9-12 mm).
When to survey
Surveys should be completed when the species is flowering, typically from late May through mid July, although flowering can continue until early September, depending on conditions. Coast Range populations generally flower later and senesce earlier than Willamette Valley populations.
Willamette Valley populations of Nelson’s checkermallow are typically found in open prairie remnants along the margins of streams, sloughs, ditches, roadsides, fence rows, and drainage swales and in fallow fields. Occasionally, the species occurs in the understory or at the edges of ash woodlands or among woody shrubs. Substrates at Willamette Valley sites range from gravelly, well drained loams to poorly drained, hydric clay soils. Coast Range populations often occur in open areas in wet to dry meadows and intermittent stream channels, and on the edges of coniferous forests in substrates ranging from clay to loam. The species is found at elevations from about 43-610 m (140-2000 ft).
Commonly associated native plant species include Achillea millefolium, Carex spp., Crataegus spp., Deschampsia caespitosa, Equisetum arvense, Fragaria virginiana, Fraxinus latifolia, Galium aparine, Geum macrophyllum, Heracleum lanatum, Hordeum brachyantherum, Juncus spp., Lupinus polyphyllus, Madia sativa, Prunella vulgaris, Pteridium aquilinum, Quercus garryana, Senecio triangularis, Spiraea douglasii, Symphoricarpos albus, and Triteleia hyacinthina. Common non-native associates include Alopecurus pratensis, Arrhenatherum elatius, Cirsium spp., Dactylis glomerata, Daucus carota, Holcus lanatus, Hypericum perforatum, Hypochaeris radicata, Leucanthemum vulgare, Lotus corniculatus, Parentucellia viscosa, Phalaris arundinacea, Phleum pratense, Rosa spp., Rubus spp., Schedonorus arundinaceus, Senecio jacobaea, and Vicia spp.
Nelson’s checkermallow occurs in the Willamette Valley and on the western flanks of the Coast Range, from southern Benton County, Oregon north to Lewis County, Washington. The majority of populations occur in Oregon, with many concentrated near the cities of Corvallis and Salem. Only two populations are known from Washington, one from Cowlitz County and one from Lewis County.
The species was reported from Clatsop County, Oregon in 1999. However, this putative occurrence requires further investigation, as the report was based on an unvouchered sighting of a single plant, and no Sidalcea plants were detected during a 2005 visit to the site.
Benton, Clackamas, Columbia, Linn, Marion, Polk, Tillamook, Washington, Yamhill
Major threats to this species include habitat loss due to agricultural and urban development, ecological succession resulting in the encroachment of trees and woody shrubs into open prairie habitats, and exotic weed invasions. Seed survival in many populations of Nelson’s checkermallow is severely limited by pre-dispersal seed predation by native, host-specific weevils (Macrorhoptus sidalceae). The weevils seem to be restricted to the Willamette Valley, southwestern Washington, and lower Coast Range; there are no reports of the parasite from Coast Range populations of Nelson’s checkermallow in Yamhill, Tillamook, and Washington Counties. Additional threats include possible inbreeding depression due to small population sizes and habitat fragmentation, and interspecific hybridization.
A U.S. Fish and Wildlife Service Recovery Plan for the threatened Nelson's checkermallow (Sidalcea nelsoniana) was released in 1998.
A U.S. Fish and Wildlife Service Recovery Plan for prairie species of western Oregon and southwestern Washington (pdf document, 9.63 MB) was released in 2010 and addresses updated conservation needs of Nelson’s checkermallow.
Did you know?
Nelson’s checkermallow is strongly outcrossing, as perfect-flowered plants are protandrous (in individual flowers, pollen matures before the stigmas are receptive), and female plants are obligately outcrossed (they must be fertilized with pollen from other plants, as they produce no pollen of their own). Most Willamette Valley populations have a far greater number of female plants than perfect plants.
The species can also spread vegetatively by rhizomes that form multiple crowns with distinct clusters of stems, making it difficult to distinguish individual plants.
Current/Recent ODA projects
Developing population density estimates for nine rare Willamette Valley prairie species (pdf, 5.33 MB)
Currin, R., M. Carr, and R. Meinke. 2008. Developing population density estimates for nine rare Willamette Valley prairie species. Report prepared for U.S. Fish and Wildlife Service, Region 1, Portland, Oregon. Oregon Department of Agriculture, Salem, Oregon.
Halse, R. R., B. A. Rottink, and R. Mishaga. 1989. Studies in Sidalcea taxonomy. Northwest Science 63:154-161.
Hitchcock, C. L., A. Cronquist, M. Ownbey, and J. W. Thompson. 1961. Vascular plants of the Pacific Northwest. Part 3: Saxifragaceae to Ericaceae. University of Washington Press, Seattle.
Meinke, R.J. 1982. Threatened and endangered vascular plants of Oregon: An illustrated guide. Unpublished report for the U.S. Fish and Wildlife Service, Region 1, Portland, Oregon. Oregon Department of Agriculture, Salem, Oregon.
ORBIC (Oregon Biodiversity Information Center). 2010a. Rare, threatened and endangered species of Oregon. Institute for Natural Resources, Portland State University, Portland, Oregon.
ORBIC (Oregon Biodiversity Information Center). 2010b. ORBIC element occurrence database. Portland, Oregon.
USFWS (U.S. Fish and Wildlife Service). 1993. Determination of threatened status for the plant Sidalcea nelsoniana
(Nelson's checker-mallow). Federal Register 58:8235-8243. Available at http://ecos.fws.gov/docs/federal_register/fr2222.pdf
(pdf document, 2.80 MB). Accessed September 1, 2011.
USFWS. 1998. Recovery Plan for the threatened Nelson's checker-mallow (Sidalcea nelsoniana). Portland, Oregon: U.S. Fish and Wildlife Service. p.61.
USFWS (U.S. Fish and Wildlife Service). 2010. Recovery Plan for the prairie species of western
Oregon and southwestern Washington. U.S. Fish and Wildlife Service, Portland,