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.
- 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.
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.
Ecology and wildlife value
A sandy-soil specialist of the Colorado Plateau, used by monarchs and queens moving through canyon country in spring.
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.
Distribution is generalized to state level. For county-level maps 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.
- Plants of the World Online 21286-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3574177. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 898625. Community observations, photographs and phenology.
- Wikipedia. General-audience article on this species.
- BONAP county distribution map. Biota of North America Program. County-level range map.
- NatureServe Explorer. Conservation status ranks at global and state level.
- World Flora Online. Nomenclature and synonymy.
- 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
- 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
- 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
- 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
- USDA, NRCS (2026). The PLANTS Database. National Plant Data Team, Greensboro, North Carolina. State-level distribution, wetland status and nomenclature. View
- 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
Cite this page
This page is licensed CC BY 4.0. Quote it, adapt it and reuse it, including commercially, as long as you credit Milkweed USA and link back.
Milkweed USA. (2026). Ruth’s Milkweed (Asclepias ruthiae). Retrieved DATE, from https://milkweedusa.com/species/ruths-milkweed/
"Ruth’s Milkweed (Asclepias ruthiae)." Milkweed USA, 2026, https://milkweedusa.com/species/ruths-milkweed/. Accessed DATE.
Milkweed USA. "Ruth’s Milkweed (Asclepias ruthiae)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/ruths-milkweed/.
@misc{milkweedusa_speciesruthsmilkweed,
title = {Ruth’s Milkweed (Asclepias ruthiae)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/ruths-milkweed/},
note = {Accessed DATE}
}