Zion Milkvetch Astragalus zionis
Zion Milkvetch is a perennial wildflower native to the lower 48 states. It blooms Apr – Jun. A host for pollen-specialist native bees.
More about this plant
Astragalus zionis is a species of legume known by the common name Zion milkvetch. It is one of the earliest flowers to bloom in Zion canyon. First described by botanist Marcus E. Jones in 1895, the species has also been placed in the defunct genus Xylophacos under the name Xylophacos zionis. The variety Astragalus zionis var. vigulus, the guard milkvetch, was described by Stanley Welsh in 1993. Wikipedia →
Growing & care
USDA PLANTS · TRY- Hardiness
- ≥ zone 8 derived from its U.S. range
- Lifespan
- Perennial
- Flower colour
- Purple 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 · 4 bee visitors
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.
4 native & managed bee species are documented visiting Zion Milkvetch :
Related plants
More Astragalus →
How we know this (2) 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.
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 (18) 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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