Asclepias asperula

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Antelope horns
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Gentianales
Family: Apocynaceae
Genus: Asclepias
A. asperula
Binomial name
Asclepias asperula
(Decne.) Woodson
  • Acerates asperula Decne.
  • Asclepias capricornu Woodson
  • Asclepias decumbens (Nutt.) K.Schum. nom. illeg.
  • Asclepiodora asperula (Decne.) E.Fourn.
  • Asclepiodora decumbens (Nutt.) A.Gray

Asclepias asperula is a species of milkweed native to the Southwestern United States and northern Mexico. Its common names include antelope horns, green-flowered milkweed, and spider antelope horns.


It is a perennial plant growing to 0.3–0.9 m (1–3 feet) tall, with clustered greenish-yellow flowers with maroon highlights. It blooms from April through June, and favors quickly-draining soil that is higher in inorganic matter, such as sand and rock chips. It can grow in loam and clay, if provided with adequate drainage and frequent-enough dryness.[2] Moisture level demands and tolerance depend upon the subspecies and possibly ecotype. The plant has a deep taproot so it needs to have the deepest-possible pot if grown in a container and should not be waterlogged.[2]

Asclepias asperula is divided into two subspecies: asperula and capricornu (also known as var. decumbens), with the latter occurring in moister conditions and having wider leaves. This helps to explain conflicting information about cold hardiness, moisture tolerance, and cardenolide levels when many sources are compared that do not mention the subspecies division. Subspecies asperula occurs in drier and hotter habitat, thus its narrower leaves and lower maximum height. It likely also has a higher cardenolide level and lower tolerance of colder growing zones than subspecies capricornu. Subspecies asperula may be referred to colloquially as "spider milkweed" and subspecies capricornu may be referred to colloquially as "antelope horns". However, sometimes subspecies asperula is also referred to as antelope horns.[3][4]

This species may require a species of solitary bee that is large and strong enough to be able to pry open its flowers for successful pollination.[5]

Monarch butterflies[edit]

Like several other species of milkweed, A. asperula is a food for monarch butterfly caterpillars. Along with being a source of nutrition for monarchs, the plants also contain toxic cardiac glycosides (Cardenolides) that the monarchs retain, making them unpalatable and poisonous to predators. For the same reason, A. asperula can be poisonous to livestock and other animals, including humans.


  1. ^ "The Plant List: A Working List of All Plant Species". Retrieved 12 April 2015.
  2. ^ a b "Asclepias asperula — Antelope Horn". Plant Finder. Native American Seed. 2019. Retrieved 21 January 2019.
  3. ^ "Asclepias asperula subsp. asperula". The Jepson Herbarium. Regents of the University of California. 2019. Retrieved 21 January 2019.
  4. ^ "Asclepias asperula ssp. capricornu". Lady Bird Johnson Wildflower Center. The University of Texas at Austin. 2019. Retrieved 21 January 2019.
  5. ^ "Asclepias asperula". Lady Bird Johnson Wildflower Center. The University of Texas at Austin. 2019. Retrieved 21 January 2019.

External links[edit]