Prostrate Milkweed
Asclepias prostrata W.H. Blackwell
A federally endangered milkweed known from a few sites in the south Texas brush country, growing completely flat against gravelly ground with small greenish-white flowers. It was listed under the Endangered Species Act in 2023.
- Height
- 2 in–6 in
- Spread
- 8 in–1.7 ft
- Flowers
- green, white
- Bloom
- March to September
- Light
- Full sun
- Soil moisture
- Dry
- USDA zones
- 8–10
- Leaves
- Opposite, narrow
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 30 days cold-moist
- Range
- 1 state
When it flowers
Prostrate Milkweed blooms March to September, peaking in April and May.
How to identify it
- Entirely prostrate, with stems lying flat on bare gravelly soil.
- Small narrow opposite leaves and tiny greenish-white flowers.
- Known only from Starr and Zapata counties in south Texas and adjacent Mexico.
Ecology and wildlife value
Threatened by brush clearing, energy development and border infrastructure. Most surviving populations are tiny.
Growing prostrate milkweed
Federally endangered. Collection is prohibited; report sightings to Texas Parks and Wildlife.
Seed needs about 30 days of cold-moist stratification. Deep taproot, resents transplanting. See how to plant milkweed seed for the full method.
Cautions
Listed as Endangered under the US Endangered Species Act. More on milkweed toxicity.
Where prostrate milkweed grows
Recorded in 1 state: Texas.
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 21269-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170330. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 158755. 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
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Milkweed USA. (2026). Prostrate Milkweed (Asclepias prostrata). Retrieved DATE, from https://milkweedusa.com/species/prostrate-milkweed/
"Prostrate Milkweed (Asclepias prostrata)." Milkweed USA, 2026, https://milkweedusa.com/species/prostrate-milkweed/. Accessed DATE.
Milkweed USA. "Prostrate Milkweed (Asclepias prostrata)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/prostrate-milkweed/.
@misc{milkweedusa_speciesprostratemilkweed,
title = {Prostrate Milkweed (Asclepias prostrata)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/prostrate-milkweed/},
note = {Accessed DATE}
}