Serpentine Milkweed
Asclepias solanoana Woodson
A prostrate northern California endemic confined to serpentine barrens, forming flat mats of round gray-green leaves studded with small cream flowers. It grows on soil so metal-rich that almost nothing else survives.
Also called Solano Milkweed.
- Height
- 4 in–10 in
- Spread
- 1 ft–2 ft
- Flowers
- cream, pink
- Bloom
- May to July
- Light
- Full sun
- Soil moisture
- Dry
- USDA zones
- 7–9
- Leaves
- Opposite, orbicular
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 60 days cold-moist
- Range
- 1 state
When it flowers
Serpentine Milkweed blooms May to July, peaking in June.
How to identify it
- Completely prostrate mats on bare serpentine rock and soil.
- Round, thick, gray-green leaves pressed to the ground.
- Small cream flowers with pinkish hoods.
Ecology and wildlife value
A serpentine-endemic rarity of high conservation value and very limited distribution.
Growing serpentine milkweed
Should not be collected or cultivated from wild material.
Seed needs about 60 days of cold-moist stratification. Deep taproot, resents transplanting. See how to plant milkweed seed for the full method.
Cautions
Rare California endemic; leave undisturbed. More on milkweed toxicity.
Where serpentine milkweed grows
Recorded in 1 state: California.
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 290390-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170277. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 62293. 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). Serpentine Milkweed (Asclepias solanoana). Retrieved DATE, from https://milkweedusa.com/species/serpentine-milkweed/
"Serpentine Milkweed (Asclepias solanoana)." Milkweed USA, 2026, https://milkweedusa.com/species/serpentine-milkweed/. Accessed DATE.
Milkweed USA. "Serpentine Milkweed (Asclepias solanoana)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/serpentine-milkweed/.
@misc{milkweedusa_speciesserpentinemilkweed,
title = {Serpentine Milkweed (Asclepias solanoana)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/serpentine-milkweed/},
note = {Accessed DATE}
}