Antelope Horns
Asclepias asperula (Decne.) Woodson
A low, sprawling clump of arching stems topped by softball-sized globes of green flowers with maroon centers, blooming very early on limestone and caliche soils. In Texas and New Mexico it is the plant that meets the first northbound monarchs of the year.
Also called Spider Milkweed, Green-flowered Milkweed.
- Height
- 1 ft–2 ft
- Spread
- 1.5 ft–3 ft
- Flowers
- green, cream, maroon
- Bloom
- March to July
- Light
- Full sun
- Soil moisture
- Dry
- USDA zones
- 5–9
- Leaves
- Alternate, narrow
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 30 days cold-moist
- Range
- 9 states
When it flowers
Antelope Horns blooms March to July, peaking in April and May.
How to identify it
- Flowers in tight spherical clusters, pale green with dark red-purple hoods. No other milkweed in its range looks like this.
- Stems sprawl outward and curve upward rather than standing straight.
- Leaves are long, narrow and often folded lengthwise along the midrib.
- Curved, upward-pointing pods gave the plant its name.
Ecology and wildlife value
Critically timed rather than merely abundant: it is in full leaf in March and April when monarchs arrive in Texas from Mexico, making it a keystone host for the first generation of the year. Also heavily used by queen butterflies.
Growing antelope horns
Demands lean, alkaline, sharply drained soil and full sun; it rots quickly in rich beds or irrigated lawns. Direct-sow into gravelly ground, because the taproot resents transplanting. Goes dormant by late summer.
Seed needs about 30 days of cold-moist stratification. Deep taproot, resents transplanting. See how to plant milkweed seed for the full method.
Cautions
One of the more toxic species to livestock, historically responsible for sheep losses on overgrazed range. More on milkweed toxicity.
Where antelope horns grows
Recorded in 9 states: Arizona, Colorado, Kansas, Nebraska, New Mexico, Nevada, Oklahoma, Texas, Utah.
Distribution is generalized to state level. For county-level maps see USDA PLANTS and BONAP.
Frequently asked questions
When do antelope horns bloom in Texas?
Typically March through May, with a possible second flush after summer rain. That early bloom is what makes it so important to the first northbound monarch generation.
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 21143-2. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 8683730. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 62298. 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). Antelope Horns (Asclepias asperula). Retrieved DATE, from https://milkweedusa.com/species/antelope-horns/
"Antelope Horns (Asclepias asperula)." Milkweed USA, 2026, https://milkweedusa.com/species/antelope-horns/. Accessed DATE.
Milkweed USA. "Antelope Horns (Asclepias asperula)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/antelope-horns/.
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title = {Antelope Horns (Asclepias asperula)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/antelope-horns/},
note = {Accessed DATE}
}