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Ruth’s Milkweed

Asclepias ruthiae Maguire

A low, spreading Colorado Plateau milkweed of red sand and slickrock country, with small thick leaves and pale pink-cream flowers held close to the ground among the sandstone.

Ruth’s Milkweed (Asclepias ruthiae) in flower, showing pink and cream blooms in rounded clusters above opposite ovate leaves
Brad Grimm · CC BY 4.0 · Wikimedia Commons
Height
4 in–1 ft
Spread
10 in–2 ft
Flowers
pink, cream
Bloom
April to June
Light
Full sun
Soil moisture
Dry
USDA zones
5–9
Leaves
Opposite, ovate
Sap
Milky latex
Roots
Deep taproot, resents transplanting
Stratification
60 days cold-moist
Range
3 states

When it flowers

Ruth’s Milkweed blooms April to June, peaking in May.

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How to identify it

  • Prostrate to low-spreading stems radiating from a central taproot.
  • Small, thick, blunt leaves, often folded and gray-tinged.
  • Pale pink to cream flowers in small clusters near the stem tips.

Unfamiliar words are in the glossary, and the identification key will narrow a plant down from what you can see.

Diagram of Ruth’s Milkweed showing opposite ovate leaves and pink flower clusters
Diagnostic plate Drawn from this species' own characters: opposite leaves, ovate in shape, sprawling, with pink to cream umbels. Sap is milky.

The parts that identify it

Flower of Ruth’s Milkweed (Asclepias ruthiae)
Flower. Brad Grimm · CC BY 4.0 · Wikimedia Commons
Ruth’s Milkweed (Asclepias ruthiae). Asclepias uncialis subsp. ruthiae kz02
Kenraiz · CC BY-SA 4.0 · Wikimedia Commons
Ruth’s Milkweed (Asclepias ruthiae). Asclepias uncialis subsp. ruthiae kz01
Kenraiz · CC BY-SA 4.0 · Wikimedia Commons
Ruth’s Milkweed (Asclepias ruthiae). Ruth’s Milkweed photographed in Emery County, US-UT, US
Parker James Lloyd · CC BY 4.0 · iNaturalist
Ruth’s Milkweed (Asclepias ruthiae). Ruth’s Milkweed photographed in Utah, US
Kenzie Anderson-Bell · CC BY 4.0 · iNaturalist
Ruth’s Milkweed (Asclepias ruthiae). Ruth’s Milkweed photographed in Emery, Utah, United States
Matt Berger · CC BY 4.0 · iNaturalist
Ruth’s Milkweed (Asclepias ruthiae). Ruth’s Milkweed photographed in Wayne County, US-UT, US
Public domain (CC0) · CC0 · iNaturalist
Ruth’s Milkweed (Asclepias ruthiae). Ruth’s Milkweed photographed in Huntington, UT, US
Dee Shea Himes · CC BY 4.0 · iNaturalist

Ecology and wildlife value

A sandy-soil specialist of the Colorado Plateau, used by monarchs and queens moving through canyon country in spring.

Monarchs are not the only thing that will find it. Expect large milkweed bugs on ripening pods, oleander aphids on the stems, red milkweed beetles at the flowers and, in late summer, milkweed tussock moths. Everything that lives on milkweed.

Growing ruth’s milkweed

Rarely available. Needs pure sand, full exposure and no summer irrigation.

Seed needs about 60 days of cold-moist stratification. Deep taproot, resents transplanting. See how to plant milkweed seed for the full method.

Cautions

Standard milkweed cautions. More on milkweed toxicity.

Where ruth’s milkweed grows

Recorded in 3 states: Arizona, Nevada, Utah.

Alaska: not recorded Maine: not recorded Vermont: not recorded New Hampshire: not recorded Washington: not recorded Idaho: not recorded Montana: not recorded North Dakota: not recorded Minnesota: not recorded Illinois: not recorded Wisconsin: not recorded Michigan: not recorded New York: not recorded Massachusetts: not recorded Rhode Island: not recorded Oregon: not recorded Nevada: recorded Wyoming: not recorded South Dakota: not recorded Iowa: not recorded Indiana: not recorded Ohio: not recorded Pennsylvania: not recorded New Jersey: not recorded Connecticut: not recorded California: not recorded Utah: recorded Colorado: not recorded Nebraska: not recorded Missouri: not recorded Kentucky: not recorded West Virginia: not recorded Virginia: not recorded Maryland: not recorded Delaware: not recorded Arizona: recorded New Mexico: not recorded Kansas: not recorded Arkansas: not recorded Tennessee: not recorded North Carolina: not recorded South Carolina: not recorded District of Columbia: not recorded Texas: not recorded Oklahoma: not recorded Louisiana: not recorded Mississippi: not recorded Alabama: not recorded Georgia: not recorded Hawaii: not recorded Florida: not recorded
Recorded in 3 states. Shading is generalized to whole states.

USDA PLANTS holds no county-level records for this species, so the map above is generalized to whole states. For what county data exists see USDA PLANTS and BONAP.

References and further reading

Names, ranges and conservation status here are drawn from the databases below. Where those disagree with a regional flora, trust the flora.

  1. Plants of the World Online 21286-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
  2. GBIF 3574177. Global Biodiversity Information Facility. Aggregated occurrence records.
  3. iNaturalist 898625. Community observations, photographs and phenology.
  4. Wikipedia. General-audience article on this species.
  5. BONAP county distribution map. Biota of North America Program. County-level range map.
  6. NatureServe Explorer. Conservation status ranks at global and state level.
  7. World Flora Online. Nomenclature and synonymy.
  8. Woodson, R. E. (1954). The North American species of Asclepias L.. Annals of the Missouri Botanical Garden 41(1): 1–211. The monograph the modern taxonomy of the genus still rests on. View
  9. Flora of North America Editorial Committee (eds.) (2026). Flora of North America North of Mexico. Oxford University Press, New York and Oxford. Accepted names, keys and descriptions for the North American flora. View
  10. Royal Botanic Gardens, Kew (2026). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Nomenclature and global distribution, keyed to IPNI name identifiers. View
  11. Kartesz, J. T. (Biota of North America Program) (2026). North American Plant Atlas. BONAP, Chapel Hill, North Carolina. County-level distribution maps, the basis for the ranges generalized here. View
  12. USDA, NRCS (2026). The PLANTS Database. National Plant Data Team, Greensboro, North Carolina. State-level distribution, wetland status and nomenclature. View
  13. Agrawal, A. A. (2017). Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Princeton University Press. The standard general account of the milkweed and monarch relationship. View

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APA Milkweed USA. (2026). Ruth’s Milkweed (Asclepias ruthiae). Retrieved DATE, from https://milkweedusa.com/species/ruths-milkweed/
MLA "Ruth’s Milkweed (Asclepias ruthiae)." Milkweed USA, 2026, https://milkweedusa.com/species/ruths-milkweed/. Accessed DATE.
Chicago Milkweed USA. "Ruth’s Milkweed (Asclepias ruthiae)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/ruths-milkweed/.
BibTeX @misc{milkweedusa_speciesruthsmilkweed, title = {Ruth’s Milkweed (Asclepias ruthiae)}, author = {{Milkweed USA}}, year = {2026}, url = {https://milkweedusa.com/species/ruths-milkweed/}, note = {Accessed DATE} }