SafePlants

California Milkweed (Asclepias californica)

California Milkweed, scientifically known as Asclepias californica, is a vital plant for monarch butterflies, serving as the primary host for their caterpillars. Its increasing popularity in drought-tolerant gardens is providing much-needed support for these struggling insects.

Considerations for Pets

• Milkweed is named for its milky sap, which consists of a latex.

Nomenclature and Taxonomy

• Scientific Name: Asclepias californica
• Common Names: California Milkweed, Round-hood Milkweed
• Family: Asclepiadaceae (Milkweed Family)
• Taxonomic Rank: Subspecies - Asclepias californica Greene subsp. californica

Distribution and Habitat

• Native to California, Nevada, and Oregon.
• Specifically found throughout lower northern, central, and southern California.
• Prefers rocky soil.
• Thrives in USDA hardiness zones 7a-10b.

Ecological Role

• Essential host plant for monarch butterfly caterpillars, their only food source.
• The decline of native milkweeds has contributed to the decline of monarch butterfly populations.
• Exotic milkweed species may disrupt monarch migration patterns.
• Important to plant milkweed at least ten miles from monarch overwintering sites.

Morphological Characteristics

• Perennial plant with silvery foliage and showy, pale pink flowers.
• Grows to a height of 1 to 3 feet.
• Flowers are medium-sized, 1-2 inches, in inflorescences greater than 5 inches.

Interactions with Other Organisms

• Serves as the exclusive host plant for monarch butterfly caterpillars.

Quirky Facts

• Attempts to use milkweed down in cloth-making date back to the 1600s.

Further Information

• Seeds are available for sale in California, Oregon, Washington, Idaho, Nevada, and Utah.
• Available at Armstrong Garden Centers in Southern California.
• University of California Agriculture and Natural Resources is a resource.