Slimleaf Milkweed
Asclepias stenophylla A. Gray
A tall wand of a plant with grass-fine leaves and creamy-green flowers clustered tight against the stem, scattered through unplowed tallgrass and mixed-grass prairie.
Also called Narrow-leaf Green Milkweed.
- Height
- 1.5 ft–3.3 ft
- Spread
- 10 in–1.5 ft
- Flowers
- cream, green
- Bloom
- June to August
- Light
- Full sun
- Soil moisture
- Dry
- USDA zones
- 4–8
- Leaves
- Alternate, threadlike
- Sap
- Milky latex
- Roots
- Deep taproot, resents transplanting
- Stratification
- 30 days cold-moist
- Range
- 13 states
When it flowers
Slimleaf Milkweed blooms June to August, peaking in July.
How to identify it
- Extremely narrow alternate leaves, sometimes eight inches long and only a few millimeters wide.
- Flowers greenish-cream in small axillary clusters up the stem.
- Reliable indicator of high-quality remnant prairie.
Unfamiliar words are in the glossary, and the identification key will narrow a plant down from what you can see.
The parts that identify it
Ecology and wildlife value
A prairie-remnant specialist; its presence usually signals ground that has never been plowed.
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 slimleaf milkweed
Rarely available; needs lean prairie soil and patience.
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 slimleaf milkweed grows
Recorded in 13 states: Arkansas, Colorado, Iowa, Kansas, Louisiana, Missouri, Montana, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, Wyoming.
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 94664-1. Royal Botanic Gardens, Kew. Accepted name, authorship and global distribution.
- GBIF 3170321. Global Biodiversity Information Facility. Aggregated occurrence records.
- iNaturalist 158760. 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). Slimleaf Milkweed (Asclepias stenophylla). Retrieved DATE, from https://milkweedusa.com/species/slimleaf-milkweed/
"Slimleaf Milkweed (Asclepias stenophylla)." Milkweed USA, 2026, https://milkweedusa.com/species/slimleaf-milkweed/. Accessed DATE.
Milkweed USA. "Slimleaf Milkweed (Asclepias stenophylla)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/species/slimleaf-milkweed/.
@misc{milkweedusa_speciesslimleafmilkweed,
title = {Slimleaf Milkweed (Asclepias stenophylla)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/species/slimleaf-milkweed/},
note = {Accessed DATE}
}