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Home / Browse / Asclepias / Ruth's Milkweed (subsp. ruthiae)
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Pictured: Asclepias uncialis — the species. This subspecies isn’t separately illustrated.
Asclepiadaceae family

Ruth's Milkweed (subsp. ruthiae) Asclepias uncialis subsp. ruthiae subspecies

Native ★ Monarch host plant

Ruth's Milkweed (subsp. ruthiae) is a perennial wildflower native to the lower 48 states. Monarch host plant.

More about this plant

Asclepias uncialis is a species of flowering plant in the dogbane family known by the common name wheel milkweed. It is native to the western United States. Two subspecies are sometimes described, with ssp. ruthiae containing three plants which are sometimes described as separate species, Asclepias ruthiae, A. eastwoodiana, and A. sanjuanensis. Wikipedia →

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
Cold hardiness (derived) — Hardiness
Hardiness
≥ zone 8 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 →
★ Monarch Larval host plant

A monarch host plant.

Monarch caterpillars eat only milkweeds (Asclepias). As a native milkweed, Ruth's Milkweed (subsp. ruthiae) is a documented larval host across its breeding range.

Find milkweed near you Journey North migration map →
Host status from PlantKey's open monarch-host overlay · migration data via Journey North (link)
❧ Caterpillar hosts ~12 caterpillar species

Asclepias supports ~12 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 Asclepias in North America, including:

Agathodes designalis · snout moth Cycnia inopinatus · tiger moth Cycnia pudens · tiger moth Cycnia tenera · Delicate Cycnia Danaus eresimus · Soldier Danaus gilippus · Queen
+ 8 more species →
Danaus plexippus · Monarch Ectypia clio · Clio Tiger Moth Euchaetes egle · Milkweed Tussock Moth Euchaetes elegans · Elegant Tussock Moth Hyalophora cecropia · Cecropia Moth Lerina incarnata · Crimson-Bodied Lichen Moth Lycorea cleobaea · brush-footed butterfly Papaipema nebris · Stalk Borer
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).
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 (11) 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
[06] Description — Wikipedia (CC BY-SA)
[07] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts · Asclepias host rule
[08] Cold hardiness (derived) — Derived from U.S. range × USDA PHZM zones
[09] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[10] Caterpillar species — NHM HOSTS (CC0)
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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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