- Kingdom - Plantae– Plants
- Subkingdom - Tracheobionta– Vascular plants
- Superdivision - Spermatophyta– Seed plants
- Division - Magnoliophyta– Flowering plants
- Class - Magnoliopsida– Dicotyledons
- Subclass - Dilleniidae
- Order - Malvales
- Family - Malvaceae– Mallow family
- Genus - Sidalcea A. Gray– checkerbloom
- Species - Sidalcea nelsoniana Piper– Nelson's checkerbloom
Perennial herb with a stout taproot and short woodstock, stems 16 to 40 inches tall, glabrous to hirsute with short appressed simple hairs; racemes spikelike but elongate and open, many-flowered, the pedicels usually about 1/8 inch long; calyx 1/8 to 1/4 inch long, usually purplish-tinged, subglabrous to fairly thickly pubescent with tiny stellae; petals 1/4 to 5/8 inch long, pinkish-lavender.
Flowering can occur as early as mid-May and extend into September, depending on weather and site conditions. Fruits have been observed as early as mid-June and as late as mid-October.
Regional endemic; southern Benton County, Oregon, north to Lewis County, Washington, and from central Linn County, Oregon, west to just west of the crest of the Coast Range. In WA it occurs in the Olympic Peninsula and Southwest Washington physiographic province.
It occurs along streams and in meadows and other relatively open areas, such as roadsides. It is generally found in areas where prairie or grassland remnants persist, such as along fencerows, drainage swales, and at the edges of plowed fields adjacent to wooded areas. Standing water is present at some sites.
Unknown. Only two populations exist in Washington, one each in Lewis and Cowlitz counties.