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Fabaceae family

Narrowleaf Milkvetch Astragalus pectinatus

Native Specialist-bee host

Narrowleaf Milkvetch is a perennial wildflower native to Canada and the lower 48 states. It blooms May – Jun. A host for pollen-specialist native bees.

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
Cold hardiness (derived) — Hardiness
Hardiness
≥ zone 4 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 →
Nitrogen fixer — Fixes atmospheric nitrogen through root-nodule bacteria — builds soil fertility for itself and its neighbours, cutting fertiliser need.Open guide →
derived roles
The garden year bloom → fruit → fall colour
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F
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A
M
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J
A
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Bloom
Bloom (the flower's colour)
Bloom · May – Jun — 180 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:

Walshia amorphella · cosmet moth ✦ Argyrotaenia franciscana · Orange Tortrix Autographa californica · Alfalfa Looper Moth Colias alexandra · Queen Alexandra's Sulphur Colias boothii · white / sulphur butterfly Colias christina · Christina Sulphur
+ 8 more species →
Colias eurytheme · Orange Sulphur 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
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). ✦ = recorded on this exact species.
✦ Bees specialist-bee host · 2 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 →

2 native & managed bee species are documented visiting Narrowleaf Milkvetch :

Bombus huntii · Hunt Bumble Bee Bombus nevadensis · Nevada Bumble 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.
How we know this (2) Methods & honest limits
Leaf build Direct fact

We read each species’ measured specific leaf area (leaf area per unit dry weight) from the Global Spectrum dataset and band it: thin & fast (high SLA), medium, or thick & tough (low SLA). The global median is about 10 mm²/mg.

Honest limits: A species-mean from pooled measurements — individual plants vary with light and site. A broad strategy signal, not a precise per-plant figure.

Díaz, S. et al. (2022) The global spectrum of plant form and function: enhanced species-level trait dataset. Scientific Data 9:755.
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 (20) 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] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts · Smith et al. 2024 (CC BY)
[09] Conservation rank — NatureServe Explorer (CC BY)
[10] Functional traits — TRY Plant Trait Database (CC BY 4.0)
[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] Nitrogen fixation — Werner et al. 2014 (Dryad, CC0)
[17] Flower-visitor value (derived) — Noori et al. 2026 (CC BY 4.0) · GloBI
[18] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[19] Caterpillar species — NHM HOSTS (CC0)
[20] 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.
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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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