Bloomipedia
Hartweg's climbing milkweed (Funastrum heterophyllum)
Photo: Isaac Ethington via iNaturalist · CC BY 4.0 · resized

Flower profile

Hartweg's climbing milkweed

Funastrum heterophyllum

Hartweg's climbing milkweed (Funastrum heterophyllum) is a vine in the Apocynaceae family, native in the lower 48 states, blooming mostly March–May across the U.S.

Native to Arizona

Hartweg's climbing milkweed is a wildflower that USDA PLANTS lists as native in the lower 48 states. In Arizona it's most often seen in bloom in March–October.

6states where USDA records it
1,849AZ sightings*
4,934U.S. sightings*

*iNaturalist research-grade observations, as of October 17, 2026.

On our lists for: Arizona

Quick look

Funastrum cynanchoides, also known as fringed twinevine, twining milkweed or climbing milkweed, is a perennial plant in the family Apocynaceae that grows twining through other plants in the Mojave Desert and Sonoran Desert. It has milky sap and smells pungent. It is similar to Funastrum hirtellum.

  • It belongs to the Apocynaceae family. iNaturalist
  • USDA PLANTS describes it as an herb (forb) / a vine with a perennial life cycle. USDA PLANTS
  • USDA PLANTS lists it as native in the lower 48 states and records it in 6 states. USDA PLANTS
  • NatureServe lists it as native to Arizona. NatureServe
  • In Arizona, most iNaturalist sightings of it in flower come in March–October. iNaturalist
  • iNaturalist has 1,849 research-grade sightings of it in Arizona, ranking #51 among the 132 flowers on our Arizona list. iNaturalist

When does it bloom?

In Arizona, most flowering sightings come in March–October.

Flowering records by month in Arizona (iNaturalist research-grade observations marked “Flowering”) (130 records)

Conservation status

Federal (U.S. ESA)
Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. USFWS ECOS
NatureServe global
T5 See NatureServe for what T5 means. NatureServe
Arizona
Not listed Not on Arizona Native Plant Law protected plants (Ariz. Admin. Code R3-3 Art. 11, App. A, eff. Feb. 2, 2025). NatureServe: SNR, not yet ranked in Arizona. AAC R3-3 App. A
Rare elsewhere
Other states where NatureServe ranks it rare or missing: NV (S2), UT (S2). (S1 critically imperiled, S2 imperiled, SH possibly extirpated, SX presumed extirpated.)

Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.

Can you eat it?

For peopleNot well documented

None of the sources we checked (NC State Extension (no page for this plant), USDA PLANTS) say whether it's edible or poisonous for people.

For petsNot well documented

It isn't on the ASPCA plant list.

🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.

Where does it grow?

USDA PLANTS records hartweg's climbing milkweed in 6 states.

recorded by USDA PLANTS on our state lists not recorded

See the full list of states

Arizona, California, Nevada, New Mexico, Texas, Utah.

Arizona counties with USDA records: Cochise, Coconino, Gila, Graham, La Paz, Maricopa, Mohave, Navajo, Pima, Pinal, Santa Cruz, Yavapai, Yuma.

Names, range and relatives

Other scientific names (synonyms in USDA PLANTS): Funastrum lineare, Philibertia heterophylla.

County records: USDA PLANTS lists it in 32 counties across 6 states; the most are in Arizona (13), California (7), Texas (5).

More from the Apocynaceae family (28 on Bloomipedia; most observed first): Common milkweed, Butterfly milkweed, Lesser periwinkle, Swamp milkweed, Greater periwinkle, Green antelopehorns, Antelopehorn milkweed, Showy milkweed.

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Sources