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horsetail milkweed
Scientific Name: Asclepias subverticillata
Family: Asclepiadaceae
Category: Dicot
Growth: Forb/herb
Duration: Perennial
Other Names:
Asclepias subverticillata
Also known as Horsetail Milkweed, Whorled Milkweed, Poison Milkweed, Bedstraw Milkweed, and western whorled milkweed, Asclepias subverticillata is a native plant with several common names reflecting its appearance and potential impact.
Considerations for Pets
- This plant is also known as poison milkweed and is referred to as being poisonous to livestock.
Considerations for Children
- This plant is also known as poison milkweed.
Taxonomy and Nomenclature
- Scientific Name: Asclepias subverticillata (A. Gray) Vail
- Family: Asclepiadaceae (Milkweed Family)
- Synonyms: Asclepias verticillata (Note: While the text suggests this is a synonym, it's crucial to recognize that Asclepias verticillata is also recognized as a distinct species, whorled milkweed)
- Common Names: Horsetail Milkweed, Whorled Milkweed, Poison Milkweed, Bedstraw Milkweed, western whorled milkweed
Distribution and Habitat
- Asclepias subverticillata is found in the central western and southwestern United States, as well as Mexico.
- It commonly grows in dense stands within pastures and areas surrounding hay.
- It also occurs occasionally throughout upland prairies.
- Primarily occurs south of Interstate 70.
- It is found in Arizona's sycamore canyon woodland habitats.
Ecological Role
- Horsetail Milkweed is considered a weedy, invasive perennial in some regions.
- It is a crucial food source for larval butterflies, especially the monarch butterfly. Female monarchs search for milkweed to lay their eggs.
Morphological Characteristics and Growth Habits
- Asclepias subverticillata is an erect-stemmed perennial rhizomatous herb, growing up to 5 feet tall, though plants can be mostly 12 to 24 inches.
- The leaves are narrow and arranged in whorls of three or paired opposite, with margins rolled backward. They are also described as soft and threadlike.
- It has rounded clusters of small white flowers that bloom in midsummer.
- It frequently has dwarf, lateral shoots in at least some of the leaf axils.
Interactions with Other Organisms
- The Horsetail Milkweed Longhorn (Tetraopes discoideus) feeds on Whorled Milkweed.
- The plant also interacts with the Black and gold bumble bee (Bombus).
- It is a deer-resistant food for larval butterflies.
Quirky Facts
- The neurotoxin is specific to the whorled-leaf types such as horsetail milkweed.
Further Information
- Dave's Garden is referenced as a resource for garden tips and ideas.
- ISM Herbarium contains distribution of Asclepias verticillata specimens.
- Discover Life has a page about the biology, natural history, ecology, identification and distribution of Asclepias subverticillata.