Arcane Milkvetch Astragalus obscurus
Arcane Milkvetch is a perennial wildflower native to the lower 48 states. It grows to 0.5 ft and blooms May – Jun. A host for pollen-specialist native bees.
More about this plant
Astragalus obscurus is a species of milkvetch known by the common name arcane milkvetch. It is native to the northwestern United States in Idaho and Oregon and northern parts of Nevada and California. It is a plant of rocky areas in mountains and Great Basin plateaus. This is a small, mat-forming perennial herb with tufts of hairy stems approaching a maximum length of 15 centimeters. The leaves are up to 10 centimeters long and made up of thick oval-shaped leaflets. The inflorescence is a dense cluster of 5 to 15 off-white to faintly lilac-tinted flowers, each less than a centimeter long. The fruit is a narrow, leathery legume pod held upright in the infructescence. It may reach 2.5 centimeters in length and usually has two chambers inside. Wikipedia →
Growing & care
USDA PLANTS · TRY- Hardiness
- ≥ zone 7 derived from its U.S. range
- Height
- 0.5 ft
- Lifespan
- Perennial
- Foliage
- Broadleaf
- Flower colour
- Yellow AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~15 caterpillar species
Astragalus supports ~15 caterpillar species.
Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a moderate genus.
Recorded feeding on Astragalus in North America, including:
+ 8 more species → ↑ show fewer
✦ Bees specialist-bee host
Specialist native bees depend on it.
Some native bees are pollen specialists (oligolectic) — they raise young only on pollen from particular plant genera. Astragalus is a recorded specialist-bee host, so losing it can mean losing the bee that relies on it.
Wildlife & visitors 1 bird
Open records of who else uses Arcane Milkvetch — a generalist food-web signal, kept separate from the keystone Ecological Value.
Recorded eaten by 1 bird species (fruit, seed, browse):
Related plants
More Astragalus →
How we know this (3) Methods & honest limits
A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.
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.
McKenzie et al. assigned each species a flower colour with a GPT-4V vision model over iNaturalist photos. We use the confident tier plus a separately-labelled lower-confidence top-up (mostly inconspicuous green/brown flowers), and render it as a small tint — never as an asserted fact, and kept out of the written synopsis.
Honest limits: AI image inference (~87% expert agreement on the confident tier); a decorative, confidence-tiered indicator, not a measured trait.
Sources for this entry (21) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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