Longhood Milkweed
Asclepias macrotis Torr.
A slender limestone-canyon milkweed of west Texas, New Mexico and southern Colorado, with thread-like leaves and small pale flowers whose unusually long hoods give it its name.
- Height
- 8 in–1.7 ft
- Spread
- 10 in–1.7 ft
- Flowers
- green, cream
- Bloom
- April to August
- Light
- Full sun
- Soil moisture
- Dry
- USDA zones
- 6–9
- Leaves
- Opposite, threadlike
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 30 days cold-moist
- Range
- 4 states
When it flowers
Longhood Milkweed blooms April to August, peaking in May and June.
How to identify it
- Very long, projecting hoods on small greenish flowers.
- Wiry sprawling stems with thread-fine opposite leaves.
- Restricted to limestone outcrops and rocky canyon slopes.
Ecology and wildlife value
A localised desert-canyon species of limited but real value to monarchs and queens moving through the Southwest.
Growing longhood milkweed
Not in 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 longhood milkweed grows
Recorded in 4 states: Arizona, Colorado, New Mexico, 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 94433-1. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170310. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 121660. 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). Longhood Milkweed (Asclepias macrotis). Retrieved DATE, from https://milkweedusa.com/species/longhood-milkweed/
"Longhood Milkweed (Asclepias macrotis)." Milkweed USA, 2026, https://milkweedusa.com/species/longhood-milkweed/. Accessed DATE.
Milkweed USA. "Longhood Milkweed (Asclepias macrotis)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/longhood-milkweed/.
@misc{milkweedusa_specieslonghoodmilkweed,
title = {Longhood Milkweed (Asclepias macrotis)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/longhood-milkweed/},
note = {Accessed DATE}
}