# San Juan Milkweed (Asclepias sanjuanensis)

> A tiny sprawling milkweed of the Four Corners sandstone country, described only in 1989, with red-violet flowers held upright on stems rarely longer than a finger. It flowers in April and May and holds one of the smallest ranges in the genus.

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

## Summary

A tiny sprawling milkweed of the Four Corners sandstone country, described only in 1989, with red-violet flowers held upright on stems rarely longer than a finger. It flowers in April and May and holds one of the smallest ranges in the genus.

## Key facts

| Field | Value |
| --- | --- |
| Scientific name | Asclepias sanjuanensis K.D. Heil, J.M. Porter & S.L. Welsh |
| Genus | Asclepias |
| Family | Apocynaceae |
| Common names | San Juan Milkweed |
| Status | Native; rare or legally protected in part of its range |
| Height | 2 in–5 in |
| Spread | 6 in–1.3 ft |
| Flower color | purple, white |
| Bloom period | April to May |
| 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) | 2 |
| Garden value (0-5) | 1 |
| Nectar value (0-5) | 2 |
| US states recorded | Arizona, New Mexico, Utah |

## Identification

- Very small and decumbent, 4 to 13 cm, with one to eight stems from a running rootstock and dense curved hairs throughout.
- Leaves lanceolate to ovate, 2 to 5 cm, short-stalked, some opposite and some alternate on the same plant, with entire rather than crinkled margins.
- Few-flowered stalkless clusters, only 3 to 8 flowers, held erect.
- Corolla red-violet; hoods red-violet on the back and white to orange at the base, each with a small tooth on either side of the tip.
- Pinyon-juniper woodland and desert scrub on sandstone between 1,400 and 1,800 m.

## Ecology

One of a group of four closely related Colorado Plateau dwarf milkweeds, alongside dwarf, large-seed, Eastwood’s and Ruth’s milkweed, that some botanists have treated as a single variable species. Flowering in April and May puts it among the earliest milkweeds anywhere in the West.

## Growing

Not in cultivation and not commercially available.

## Cautions

A narrow endemic, restricted to San Juan County in New Mexico, San Juan County in Utah, and Apache and Navajo counties in Arizona. Much of its range is on Navajo land. Photograph and report rather than collect.

## Questions

**Why is San Juan milkweed so recently described?**

It was not named until 1989, by Kenneth Heil, J. Mark Porter and Stanley Welsh, because it sits inside a group of four small Colorado Plateau milkweeds that look alike and had been lumped together. Its range turned out to be wider than first thought, reaching across northeastern Arizona and just into southeastern Utah.

## References

- Plants of the World Online: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:272735-2
- GBIF: https://www.gbif.org/species/3574140
- iNaturalist: https://www.inaturalist.org/taxa/622906
- Wikipedia: https://en.wikipedia.org/wiki/Asclepias_sanjuanensis
- BONAP county map: https://bonap.net/MapGallery/County/Asclepias%20sanjuanensis.png
- NatureServe: https://explorer.natureserve.org/Search?searchTerm=Asclepias%20sanjuanensis

## Photographs

- Asclepias sanjuanensis - Flickr - aspidoscelis (1) (Patrick Alexander from Las Cruces, NM, CC0): https://commons.wikimedia.org/wiki/File:Asclepias_sanjuanensis_-_Flickr_-_aspidoscelis_(1).jpg
- A. sanjuanensis flower (Patrick Alexander, CC0): https://commons.wikimedia.org/wiki/File:A._sanjuanensis_flower.jpg
- San Juan Milkweed photographed in 36.440 -108.305 (Public domain (CC0), CC0): https://www.inaturalist.org/observations/9259241
- San Juan Milkweed photographed in San Juan County, NM, USA (Martin Purdy, CC BY 4.0): https://www.inaturalist.org/observations/166454884
- San Juan Milkweed photographed in 36.440 -108.305 (Public domain (CC0), CC0): https://www.inaturalist.org/observations/9259241
- San Juan Milkweed photographed in San Juan County, NM, USA (Martin Purdy, CC BY 4.0): https://www.inaturalist.org/observations/166454884
- San Juan Milkweed photographed in San Juan County, NM, USA (Martin Purdy, CC BY 4.0): https://www.inaturalist.org/observations/166454884
- San Juan Milkweed photographed in San Juan County, NM, USA (Martin Purdy, CC BY 4.0): https://www.inaturalist.org/observations/166454884

## How to cite

Milkweed USA. (2026). San Juan Milkweed (Asclepias sanjuanensis). https://milkweedusa.com/species/san-juan-milkweed/