

Oldstem Idahoa Idahoa scapigera
Oldstem Idahoa is an annual wildflower native to Canada and the lower 48 states. It blooms Mar – May.
More about this plant
Idahoa is a monotypic genus of plants in the family Brassicaceae containing the single species Idahoa scapigera, which is known by the common names scalepod and oldstem idahoa. It is native to western North America from British Columbia to California to Montana where it grows generally in mountains and foothills. This is a petite annual herb growing a basal rosette of petioled leaves each one to three centimeters long and smooth or lobed along the edges. The thin, leafless erect stems rise to a maximum height near ten centimeters. Each bears a single tiny flower with white petals above red-purple sepals. The fruit is a flat, round capsule, shaped like a disc or somewhat oval, and 6 to 12 millimeters wide. The green fruit dries to a papery gray or white. Wikipedia →
Growing & care
USDA PLANTS · TRY- Hardiness
- ≥ zone 6 derived from its U.S. range
- Lifespan
- Annual
How we know this (1) Methods & honest limits
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
Sources for this entry (13) Open & cited
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