# Rusby’s Milkweed (Asclepias rusbyi)

> A slender milkweed of Arizona and New Mexico pine-oak woodland and mountain grassland, with narrow alternate leaves and small greenish-white flower clusters. It follows the summer monsoon rather than the spring.

Source: https://milkweedusa.com/species/rusbys-milkweed/  
Licence: CC BY 4.0 (Milkweed USA)

## Summary

A slender milkweed of Arizona and New Mexico pine-oak woodland and mountain grassland, with narrow alternate leaves and small greenish-white flower clusters. It follows the summer monsoon rather than the spring.

## Key facts

| Field | Value |
| --- | --- |
| Scientific name | Asclepias rusbyi (Vail) Woodson |
| Genus | Asclepias |
| Family | Apocynaceae |
| Common names | Rusby’s Milkweed |
| Status | Native |
| Height | 1 ft–2.5 ft |
| Spread | 10 in–1.7 ft |
| Flower color | green, white |
| Bloom period | May to August |
| Light | Full sun, Part shade |
| Soil moisture | Dry |
| USDA zones | 5-9 |
| Leaf arrangement | alternate |
| Leaf shape | narrow |
| Sap | Milky latex |
| Root system | Deep taproot, resents transplanting |
| Seed stratification | 30 days cold-moist |
| Monarch value (0-5) | 3 |
| Garden value (0-5) | 2 |
| Nectar value (0-5) | 2 |
| US states recorded | Arizona, New Mexico |

## Identification

- Narrow, alternate, often slightly folded leaves on a wiry upright stem.
- Small greenish-white flowers in loose clusters.
- Ponderosa pine and pine-oak woodland openings above about 5,000 feet.

## Ecology

A mid-elevation host for monarchs and queens moving through the Arizona sky islands during the monsoon.

## Growing

Not in general cultivation.

## Cautions

Standard milkweed cautions.

## References

- Plants of the World Online: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:21285-2
- GBIF: https://www.gbif.org/species/3170311
- iNaturalist: https://www.inaturalist.org/taxa/158758
- BONAP county map: https://bonap.net/MapGallery/County/Asclepias%20rusbyi.png
- NatureServe: https://explorer.natureserve.org/Search?searchTerm=Asclepias%20rusbyi

## Photographs

- Rusby’s Milkweed photographed in Canyonlands National Park, San Juan County, US-UT, US (Public domain (CC0), CC0): https://www.inaturalist.org/observations/54814011
- Rusby’s Milkweed photographed in Sonoita, AZ 85637, USA (Sue Carnahan, CC BY 4.0): https://www.inaturalist.org/observations/248605717
- Rusby’s Milkweed photographed in 86401, Kingman, AZ, US (CK2AZ, CC BY 4.0): https://www.inaturalist.org/observations/7520868
- Rusby’s Milkweed photographed in Catron County, NM, USA (Wendy McCrady, CC BY 4.0): https://www.inaturalist.org/observations/122021962
- Rusby’s Milkweed photographed in Coconino National Forest, Flagstaff, AZ, US (mark-groeneveld, CC BY 4.0): https://www.inaturalist.org/observations/125096803
- Rusby’s Milkweed photographed in Grant County, US-NM, US (Andrew Tree, CC BY 4.0): https://www.inaturalist.org/observations/239817608
- Rusby’s Milkweed photographed in Lincoln, Nevada, United States (Matt Berger, CC BY 4.0): https://www.inaturalist.org/observations/56201466

## How to cite

Milkweed USA. (2026). Rusby’s Milkweed (Asclepias rusbyi). https://milkweedusa.com/species/rusbys-milkweed/