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Fabaceae family

Humboldt County Milkvetch Astragalus agnicidus

Native Specialist-bee host

Humboldt County Milkvetch is a perennial wildflower native to the lower 48 states. A host for pollen-specialist native bees.

More about this plant

Astragalus agnicidus is a rare species of milkvetch known by the common name Humboldt County milkvetch. It is endemic to northern California, where it is known only from two populations in Humboldt County and one in Mendocino County. Wikipedia →

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
Cold hardiness (derived) — Hardiness
Hardiness
≥ zone 11 derived from its U.S. range
Size & form
Sources · Size & form
USDA PLANTS — Lifespan
Lifespan
Perennial
In the garden
Herb layer — Sits in the herb of a layered food forest or polyculture.Open guide →
derived roles
Species characteristics from USDA PLANTS (public domain) + TRY (CC BY) — general guidance, not a guarantee for your exact site. Deer "browsing" is documented palatability, not a deer-proof claim.

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:

Argyrotaenia franciscana · Orange Tortrix Autographa californica · Alfalfa Looper Moth Colias alexandra · Queen Alexandra's Sulphur Colias boothii · white / sulphur butterfly Colias christina · Christina Sulphur Colias eurytheme · Orange Sulphur
+ 8 more species →
Colias hecla · Hecla Sulphur Colias meadii · Mead's Sulphur Colias nastes · Labrador Sulphur Colias occidentalis · Western Sulphur Colias philodice · Clouded Sulphur Dicymolomia julianalis · Julia's Dicymolomia Epargyreus clarus · skipper butterfly Erynnis baptisiae · Wild Indigo Duskywing
Keystone count (genus-level) from Warren II 2026 (CC0) · Tallamy host-use records. Named species (a documented Nearctic sample, not exhaustive) from NHM HOSTS (CC0).
✦ Bees specialist-bee host · 6 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.

Xerces pollinator conservation →

6 native & managed bee species are documented visiting Humboldt County Milkvetch :

Bombus vosnesenskii · Vosnesensky Bumble Bee Bombus mixtus · Fuzzy-Horned Bumble Bee Bombus sitkensis · Sitka Bumble Bee Osmia dolerosa · mason bee Osmia laeta · mason bee Osmia tristella · mason bee
Specialist hosts from Smith et al. 2024. Visitor records (observations, not exhaustive) from Noori et al. 2026 (CC BY 4.0) · GloBI →
Species thumbnails re-hosted from iNaturalist — Creative Commons, credited per image (hover for credit). Click any species to see it on iNaturalist. Not exhaustive; many taxa have no openly-licensed photo yet.
Sources for this entry (15) Open & cited
[01] Scientific name & family — USDA PLANTS (DwCA, Zenodo 17903503)
[02] Growth habit & duration — USDA PLANTS (DwCA, Zenodo 17903503)
[03] Native status & distribution — USDA PLANTS (DwCA, Zenodo 17903503)
[04] Common name — USDA PLANTS (via GBIF)
[05] Invasive / introduced status — USDA PLANTS (DwCA, Zenodo 17903503) — native status
[07] Description — Wikipedia (CC BY-SA)
[08] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts · Smith et al. 2024 (CC BY)
[09] Conservation rank — NatureServe Explorer (CC BY)
[10] Cold hardiness (derived) — Derived from U.S. range × USDA PHZM zones
[12] Flower-visitor value (derived) — Noori et al. 2026 (CC BY 4.0) · GloBI
[13] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[14] Caterpillar species — NHM HOSTS (CC0)
[15] County range — GBIF Open Data — open-licensed occurrences (CC0/CC-BY) → county
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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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