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Asclepias asperula

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About Spider Milkweed (Asclepias asperula) 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 0.6-2 meter (1-2 feet) tall, with clustered greenish-yellow flowers with maroon highlights. It blooms from April through June, and favors moist, sandy or rocky soil. 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 alkaloids 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.
Plant Description
Plant Type
Perennial herb

Max. Height
2 - 6.6 ft (0.6 - 2 m)

Flower Color
Cream, Yellow, Green, Purple

Flowering Season
Spring, Summer, Fall

Native Status

Natural Setting
Site Type
Dry, open places, rocky places


Elevation ?
3026' - 7752'

Annual Precip. ?
6.1" - 13.0"

Summer Precip. ?
1.32" - 3.28"

Coldest Month ?
38.9° F - 51.4° F

Hottest Month ?
61.8° F - 76.9° F

Humidity ?
4.64 vpd - 29.91 vpd

Landscaping Information
Common uses
Butterfly Gardens, Bird Gardens

Nursery Availability
Rarely Available

Other Names
Common Names
Spider Antelope Horn, Green-flowered Milkweed, Antelope Horns

Sources include: Wikipedia. All text shown in the "About" section of these pages is available under the Creative Commons Attribution-ShareAlike License. Plant observation data provided by the participants of the California Consortia of Herbaria, Sunset information provided by Jepson Flora Project. Propogation from seed information provided by the Santa Barbara Botanical Garden from "Seed Propagation of Native California Plants" by Dara E. Emery. Sources of plant photos include CalPhotos, Wikimedia Commons, and independent plant photographers who have agreed to share their images with Calscape. Other general sources of information include Calflora, CNPS Manual of Vegetation Online, Jepson Flora Project, Las Pilitas, Theodore Payne, Tree of Life, The Xerces Society, and information provided by CNPS volunteer editors, with special thanks to Don Rideout. Climate data used in creation of plant range maps is from PRISM Climate Group, Oregon State University, using 30 year (1981-2010) annual "normals" at an 800 meter spatial resolution.

Links:   Jepson eFlora Taxon Page  CalPhotos  Wikipedia  Calflora

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