Rusby’s Milkweed
Asclepias rusbyi (Vail) Woodson
A slender milkweed of Arizona and New Mexico pine-oak woodland and mountain grassland, with narrow alternate leaves and small greenish-white flower clusters. It follows the summer monsoon rather than the spring.
- Height
- 1 ft–2.5 ft
- Spread
- 10 in–1.7 ft
- Flowers
- green, white
- Bloom
- May to August
- Light
- Full sun, Part shade
- Soil moisture
- Dry
- USDA zones
- 5–9
- Leaves
- Alternate, narrow
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 30 days cold-moist
- Range
- 2 states
When it flowers
Rusby’s Milkweed blooms May to August, peaking in June and July.
How to identify it
- Narrow, alternate, often slightly folded leaves on a wiry upright stem.
- Small greenish-white flowers in loose clusters.
- Ponderosa pine and pine-oak woodland openings above about 5,000 feet.
Ecology and wildlife value
A mid-elevation host for monarchs and queens moving through the Arizona sky islands during the monsoon.
Growing rusby’s milkweed
Not in general cultivation.
Seed needs about 30 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 rusby’s milkweed grows
Recorded in 2 states: Arizona, New Mexico.
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 21285-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170311. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 158758. Community observations, photographs and phenology.
- 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). Rusby’s Milkweed (Asclepias rusbyi). Retrieved DATE, from https://milkweedusa.com/species/rusbys-milkweed/
"Rusby’s Milkweed (Asclepias rusbyi)." Milkweed USA, 2026, https://milkweedusa.com/species/rusbys-milkweed/. Accessed DATE.
Milkweed USA. "Rusby’s Milkweed (Asclepias rusbyi)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/rusbys-milkweed/.
@misc{milkweedusa_speciesrusbysmilkweed,
title = {Rusby’s Milkweed (Asclepias rusbyi)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/rusbys-milkweed/},
note = {Accessed DATE}
}