# Large-seed Milkweed (Asclepias macrosperma)

> A sprawling Colorado Plateau milkweed of loose sand and dune country, only a few inches high but throwing up to twelve stems from a running rootstock, with crinkle-edged leaves, dense heads of small green and red flowers, and seeds large enough that the name refers to them.

Source: https://milkweedusa.com/species/large-seed-milkweed/  
License: CC BY 4.0 (Milkweed USA)

## Summary

A sprawling Colorado Plateau milkweed of loose sand and dune country, only a few inches high but throwing up to twelve stems from a running rootstock, with crinkle-edged leaves, dense heads of small green and red flowers, and seeds large enough that the name refers to them.

## Key facts

| Field | Value |
| --- | --- |
| Scientific name | Asclepias macrosperma Eastw. |
| Genus | Asclepias |
| Family | Apocynaceae |
| Common names | Large-seed Milkweed, Eastwood’s Milkweed |
| Status | Native |
| Height | 2 in–6 in |
| Spread | 8 in–1.7 ft |
| Flower color | green, red, yellow |
| Bloom period | April to June |
| Light | Full sun |
| Soil moisture | Dry |
| USDA zones | 5-8 |
| Leaf arrangement | opposite |
| Leaf shape | lanceolate |
| Sap | Milky latex |
| Root system | Rhizomatous, spreads by root |
| Seed stratification | 30 days cold-moist |
| Monarch value (0-5) | 3 |
| Garden value (0-5) | 1 |
| Nectar value (0-5) | 2 |
| US states recorded | Arizona, Colorado, New Mexico, Utah |

## Identification

- Low and decumbent, 6 to 15 cm, with up to twelve stems from one rootstock, densely covered in short curved hairs.
- Leaves lanceolate to lance-ovate, 2.5 to 7 cm, short-stalked, with distinctly crisped or wavy margins.
- Dense stalkless terminal clusters of 12 to 40 small flowers; green corolla tinged red, especially underneath.
- Hoods uniformly yellow to buff, not cream with a dark stripe down the back. That stripe is what separates dwarf milkweed.
- Seeds 8 to 12 mm, very large for a milkweed, in rough ovoid pods. The name macrosperma means large-seeded.

## Ecology

Confined to the Colorado Plateau, and unlike its close relatives it keeps to loose, often unstabilised sand. Flowering in April to June makes it available to monarchs moving north early, well before the summer species open.

## Growing

Not in cultivation. It needs deep moving sand and will not take garden soil.

## Cautions

Of conservation concern in Colorado, where it is known from Montezuma County only, and in New Mexico, where it is known from San Juan County only. Secure in Utah and on Navajo land in Arizona. Do not collect.

## Questions

**How is large-seed milkweed different from dwarf milkweed?**

They were long treated as one species and intermediates occur where the two ranges touch. Large-seed milkweed has broader leaves with crinkled margins, and its hoods are evenly yellow; dwarf milkweed (Asclepias involucrata) has cream hoods with a dark stripe down the back. Habitat helps too: large-seed milkweed grows on loose sand, dwarf milkweed on stable rocky or clay ground.

## References

- Plants of the World Online: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:21236-2
- GBIF: https://www.gbif.org/species/3170244
- iNaturalist: https://www.inaturalist.org/taxa/148083
- Wikipedia: https://en.wikipedia.org/wiki/Asclepias_involucrata
- BONAP county map: https://bonap.net/MapGallery/County/Asclepias%20macrosperma.png
- NatureServe: https://explorer.natureserve.org/Search?searchTerm=Asclepias%20macrosperma

## Photographs

- Asclepias macrosperma - Flickr - aspidoscelis (Patrick Alexander from Las Cruces, NM, CC0): https://commons.wikimedia.org/wiki/File:Asclepias_macrosperma_-_Flickr_-_aspidoscelis.jpg
- Asclepias macrosperma - Flickr - aspidoscelis (1) (Patrick Alexander from Las Cruces, NM, CC0): https://commons.wikimedia.org/wiki/File:Asclepias_macrosperma_-_Flickr_-_aspidoscelis_(1).jpg
- Asclepias macrosperma - Flickr - aspidoscelis (2) (Patrick Alexander from Las Cruces, NM, CC0): https://commons.wikimedia.org/wiki/File:Asclepias_macrosperma_-_Flickr_-_aspidoscelis_(2).jpg
- Asclepias macrosperma - Flickr - aspidoscelis (5) (Patrick Alexander from Las Cruces, NM, CC0): https://commons.wikimedia.org/wiki/File:Asclepias_macrosperma_-_Flickr_-_aspidoscelis_(5).jpg
- Large-seed Milkweed photographed in San Juan County, US-UT, US (Public domain (CC0), CC0): https://www.inaturalist.org/observations/24758620
- Large-seed Milkweed photographed in Vermilion Cliffs National Monument, Marble Canyon, AZ, US (Kenzie Anderson-Bell, CC BY 4.0): https://www.inaturalist.org/observations/270503664
- Large-seed Milkweed photographed in Grand Staircase-Escalante National Monument, Escalante, UT, US (Matt Berger, CC BY 4.0): https://www.inaturalist.org/observations/83732417
- Large-seed Milkweed photographed in Huntington, UT, US (Dee Shea Himes, CC BY 4.0): https://www.inaturalist.org/observations/215625089

## How to cite

Milkweed USA. (2026). Large-seed Milkweed (Asclepias macrosperma). https://milkweedusa.com/species/large-seed-milkweed/