# Utah Milkweed (Asclepias labriformis)

> A Utah endemic of the Colorado Plateau, found nowhere else on earth, and reckoned to be among the most poisonous plants on western rangeland. Creamy yellow flowers on a knee-high plant growing in dry washes where the subsoil holds water.

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

## Summary

A Utah endemic of the Colorado Plateau, found nowhere else on earth, and reckoned to be among the most poisonous plants on western rangeland. Creamy yellow flowers on a knee-high plant growing in dry washes where the subsoil holds water.

## Key facts

| Field | Value |
| --- | --- |
| Scientific name | Asclepias labriformis M.E.Jones |
| Genus | Asclepias |
| Family | Apocynaceae |
| Common names | Utah Milkweed, Labriform Milkweed |
| Status | Native; rare or legally protected in part of its range |
| Height | 1 ft–1.7 ft |
| Spread | 1 ft–1.5 ft |
| Flower color | cream, yellow, green |
| Bloom period | May to August |
| Light | Full sun |
| Soil moisture | Dry |
| USDA zones | 5-8 |
| Leaf arrangement | opposite |
| Leaf shape | lanceolate |
| Sap | Milky latex |
| Root system | Deep taproot, resents transplanting |
| Seed stratification | 30 days cold-moist |
| Monarch value (0-5) | 3 |
| Garden value (0-5) | 1 |
| Nectar value (0-5) | 3 |
| US states recorded | Utah |

## Identification

- Erect stems to about 50 cm, hairy when young and smooth with age.
- Opposite or nearly opposite leaves, leathery, up to 15 cm long and no more than 2 cm wide, with a tuft of hair at the base of the midrib.
- Faintly scented creamy yellow to yellowish-green flowers in gently domed umbels, each flower under 1 cm across.
- Dry sandy washes and sandstone canyon country between about 3,500 and 7,000 feet, from the southern Canyonlands northeast into the Uinta Basin.

## Ecology

A monarch host within its small Utah range, and a nectar source in country where midsummer flowers are scarce. Because the whole species occupies one corner of one state, its habitat matters out of all proportion to the plant's size.

## Growing

Not in the nursery trade and not a garden plant. It is listed here so that it can be recognized and left alone. If you find it, record it rather than collect it: the entire world population is in Utah.

## Cautions

Cronquist and co-authors describe this as one of the most poisonous of all western range plants, a reputation few other milkweeds carry. Treat it with real respect around livestock, and do not let it into hay. The usual milkweed advice about irritating sap applies too, but with this species the grazing risk is the serious one.

## Questions

**Is Utah milkweed really the most toxic milkweed?**

It has that reputation in the range literature, where Cronquist and co-authors call it one of the most poisonous of all western range plants. Milkweed toxicity varies enormously between species, and the narrow-leaved western group is the dangerous end of it. Utah milkweed sits at that end.

**Where can I see Asclepias labriformis?**

Only in Utah, on the Colorado Plateau, roughly from the southern Canyonlands northeast into the Uinta Basin. It grows in dry sandy washes where the subsoil stays moist.

## References

- Plants of the World Online: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:21220-2
- GBIF: https://www.gbif.org/species/3170345
- iNaturalist: https://www.inaturalist.org/taxa/126673
- BONAP county map: https://bonap.net/MapGallery/County/Asclepias%20labriformis.png
- NatureServe: https://explorer.natureserve.org/Search?searchTerm=Asclepias%20labriformis

## Photographs

- Asclepias labriformis kz02 (Kenraiz, CC BY-SA 4.0): https://commons.wikimedia.org/wiki/File:Asclepias_labriformis_kz02.jpg
- Asclepias labriformis kz03 (Kenraiz, CC BY-SA 4.0): https://commons.wikimedia.org/wiki/File:Asclepias_labriformis_kz03.jpg
- Asclepias labriformis kz01 (Kenraiz, CC BY-SA 4.0): https://commons.wikimedia.org/wiki/File:Asclepias_labriformis_kz01.jpg
- Asclepias labriformis kz04 (Kenraiz, CC BY-SA 4.0): https://commons.wikimedia.org/wiki/File:Asclepias_labriformis_kz04.jpg
- Utah Milkweed photographed in Burro Wash Trail, Teasdale, UT, US (Zach Earl, CC BY 4.0): https://www.inaturalist.org/observations/239179869
- Utah Milkweed photographed in Wayne County, UT, USA (Larry Jensen, CC BY 4.0): https://www.inaturalist.org/observations/171857836
- Utah Milkweed photographed in Cathedral Rd, Torrey, UT, US (Brad Grimm, CC BY 4.0): https://www.inaturalist.org/observations/346709756
- Utah Milkweed photographed in Wayne County, UT, USA (Brandon Corder, CC BY 4.0): https://www.inaturalist.org/observations/303906254

## How to cite

Milkweed USA. (2026). Utah Milkweed (Asclepias labriformis). https://milkweedusa.com/species/utah-milkweed/