Native rare or protectedMonarch value Garden Nectar

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.

Serpentine Milkweed (Asclepias solanoana) in flower, showing cream and pink blooms in rounded clusters above opposite orbicular leaves — Shasta-Trinity National Forest USDA Forest Service. · CC0 · Wikimedia Commons

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.

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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.

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

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

Serpentine Milkweed (Asclepias solanoana). Serpentine Milkweed photographed in California, US — Don Loarie · CC BY 4.0 · iNaturalist

Serpentine Milkweed (Asclepias solanoana). Serpentine Milkweed photographed in Mendocino National Forest, US-CA, US — Public domain (CC0) · CC0 · iNaturalist

Serpentine Milkweed (Asclepias solanoana). Serpentine Milkweed photographed in Trinity County, US-CA, US — Dee Shea Himes · CC BY 4.0 · iNaturalist

Serpentine Milkweed (Asclepias solanoana). Serpentine Milkweed photographed in Sonoma County, US-CA, US — Roger Raiche · CC BY 4.0 · iNaturalist

Ecology and wildlife value

A serpentine-endemic rarity of high conservation value and very limited distribution.

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 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.

Map of the United States with the 10 counties where Serpentine Milkweed has been recorded shaded in green — Every county with a USDA PLANTS record: **10 counties** across 1 state. An unshaded county means no record, which is not the same as absence: collection effort is uneven, and a great deal of the country has never been surveyed properly.

County records from USDA PLANTS, public domain. Cross-check against BONAP and your regional flora before making management decisions.

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

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APA

Milkweed USA. (2026). Serpentine Milkweed (Asclepias solanoana). Retrieved DATE, from https://milkweedusa.com/species/serpentine-milkweed/

MLA

"Serpentine Milkweed (Asclepias solanoana)." Milkweed USA, 2026, https://milkweedusa.com/species/serpentine-milkweed/. Accessed DATE.

Chicago

Milkweed USA. "Serpentine Milkweed (Asclepias solanoana)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/serpentine-milkweed/.

BibTeX

@misc{milkweedusa_speciesserpentinemilkweed,
  title  = {Serpentine Milkweed (Asclepias solanoana)},
  author = {{Milkweed USA}},
  year   = {2026},
  url    = {https://milkweedusa.com/species/serpentine-milkweed/},
  note   = {Accessed DATE}
}