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Fabaceae family

Brewer's Milkvetch Astragalus breweri

Native Specialist-bee host

Brewer's Milkvetch is an annual wildflower native to the lower 48 states. It blooms Apr – Jun. A host for pollen-specialist native bees.

More about this plant

Astragalus breweri is a species of milkvetch known by the common name Brewer's milkvetch. It is endemic to northern California, where it is found in several counties surrounding the north edge of the San Francisco Bay Area. It grows in open habitat in the North Coast Ranges, sometimes on serpentine soils. 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
Annual
In the garden
Herb layer — Sits in the herb of a layered food forest or polyculture.Open guide →
derived roles
The garden year bloom → fruit → fall colour
J
F
M
A
M
J
J
A
S
O
N
D
Bloom
Bloom (the flower's colour)
Bloom · Apr – Jun — 61 obs · Herbarium specimens — Park et al. 2023 (CC BY 4.0)
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

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 →
Specialist hosts from Smith et al. 2024.
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.
How we know this (1) Methods & honest limits
Climate niche (heat tolerance & native rainfall) Derived

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.

Realized-niche / climate-envelope approach (Pearson & Dawson 2003; Soberón 2007). Climate: NOAA NCEI nClimDiv county normals (1991–2020).
Derived values are computed from open data by a published method — labelled, cited, and never shown as a direct observation. Full methodology →
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)
[10] Conservation rank — NatureServe Explorer (CC BY)
[11] Climate niche — Derived — realized climate niche from U.S. county occurrences (GBIF) × NOAA NCEI county climate normals 1991–2020 (public domain)
[12] Cold hardiness (derived) — Derived from U.S. range × USDA PHZM zones
[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
Spot an error or have a better photo? Every field links to its source, and the whole dataset is open.
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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