Table of Contents for Spider Milkweed (Asclepias asperula)
Spider Milkweed (Asclepias asperula) is a herbaceous perennial that is native to the midwestern and southwestern United States, north to Idaho. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 1 to 3 feet tall, this species has greenish-yellow flowers with maroon that bloom from April to June. It is hardy in zones 5-9.
Taxonomy and Naming of Spider Milkweed (Asclepias asperula)
Spider Milkweed (Asclepias asperula) was named and described by Joseph Decaisne, a French botanist, as Acerates asperula in 1844. Later in 1954, Robert Woodson, an American botanist, renamed it to it current name of Asclepias asperula. The species has kept this name since and is a member of the Dogbane Family (Apocynaceae).
Spider Milkweed has two subspecies which include:
- Asclepias asperula ssp. asperula: located in the south-central and southwestern United States. Leaves are linear-lanceolate
- Asclepias asperula ssp. capricornu: located in the south-central and mid-western United States. Leaves are wide-lanceolate. Some treatments elevate this subspecies to the species level (Weakley 2022).
Meaning of the Scientific and Common Names
The genus name, Asclepias, is named for the Greek god of healing, Asklepios (Flora of Wisconsin). The species name, asperula, comes from the Latin word, Asperulous, which means rough.
Common Name and Alternative Names
The common name describes the look of the flowers and is a name that is a shared with the green milkweed (Asclepias viridis). One, green-flowered milkweed, is in reference to the color of the flowers. Other common names, such as antelope horns, antelopehorn milkweed, and spider antelope horn, describe the horns within the flower. Some other common names, asper milkweed (Brotherson et al. 1980 and USDA 1973) and rough milkweed (Welsh et al. 1978), are used in the state of Utah. More lesser known names for this plant include Candelit, Pleurisy Root, Trailing Milkweed, Silkweed, Immortal (Spanish use) (Edun 2009).
Physical Description of Spider Milkweed (Asclepias asperula)
- Plant Type: This plant is a herbaceous perennial.
- Height: 1 to 3 feet
- Stem: there can be several arising that are ascending or decumbent coming from the rootstock (Heil, et al. 2013)
- Leaves: The leaves are alternate to almost whorled (subopposite to alternate upwards in ssp. capricornu – Weakley 2022), simple, short-petiolate, entire, and linear-lanceolate (subsp. asperula) to wide-lanceolate (subsp. capricornu) in shape.
- Flower color: yellowish-green (Woodson 1954), hood is dark purple in ssp. asperula and cream-green in ssp. capricornu (Jepson eflora)
- Blooming period: This plant blooms from March to September.
- Fruiting type and period: This plant has follicles that mature in the late summer and fall.
Range of Spider Milkweed (Asclepias asperula) in the United States and Canada
This milkweed species overall is native to the south-central, mid-west and western United States. Subspecies asperula ranges from Texas west to California and north to Idaho. It is considered to be rare in the states of California and Idaho. This subspecies also ranges south into northern Mexico. Subspecies capricornu ranges from Texas north to Nebraska and is considered to be rare in the state of Nebraska. The Lady Bird Johnson Wildflower Center considers this to be the most common milkweed in Texas (Bibi 2014).
This species grows in open areas that are dry and rocky, sandy, or on desert swales often with scrub oaks, juniper or desert shrub. They are found on pasturelands (Karges 2018).
Other Supported Wildlife
This species is a nectar source to other butterflies, skippers, bees, and wasps during the growing season. Poling’s Hairstreak (Satyrium polingi) has noted as a frequent nectar visitor on this plant (Ferris 1980). This plant provides carbohydrates for its bee visitors (Edun 2009).
Frequently Asked Questions about Spider Milkweed (Asclepias asperula)
Is this plant poisonous?
Like other milkweeds, it has cardiac glycosides (cardenolides) and is considered to be poisonous with ingestion. Because of the poisonous nature of the plant it is deer resistant. This plant has also been listed as being poisonous to pets and livestock (Brotherson et al. 1980).
Does this plant have any ethnobotanical uses?
The Native American Ethobotanical Database shows that this plant has been used for food, veterinary uses, and for lung ailments. It has been noted to be used for dog and coyote bites (Heil, et al. 2013).
How is this plant distinguished from other milkweeds?
In the west, this species (ssp. asperula) is similar to the heart-leaf milkweed (Asclepias cordifolia), the Humboldt mountain milkweed (Asclepias cryptoceras), and the African milkweed (Asclepias fruticosa). However, all of the others have more than one leaf per node. In the east, ssp. capricornu is similar to the green milkweed (Asclepias viridis). However, the corolla lobes are longer in green milkweed – 13-17 mm as opposed to 7-12 mm long.
Is this plant invasive?
This plant has not been shown to be invasive and has a fairly restrictive habitat.
Gardening with Spider Milkweed (Asclepias asperula)
Add Spider Milkweed to Your Garden
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This species is hardy in zones 5-9. If your garden is within these zones and you have the right growing conditions (soil, moisture and exposure), you may well be able to grow this plant. However, if planted outside of its range, the hosted species may not recognize the plant or be harmed by ingesting a different species with an unfamiliar chemical composition.
This species grows best in places where it can receive full sun and has dry and/or rocky soils.
Planting This Milkweed
The seeds of this species, require a period of cold stratification in order to germinate. Because of this it is best to plant the seeds in the fall or early winter. If you get your seeds commercially, make sure that they have been cold stratified.
This species has been noted to be successful in planting from seed (Hornig 2008).
- Bibi, Wein. 2014. Royal Blues. Wildflower 31 (1): 12-19.
- Brotherson, Jack D., L.A. Szyska, and William E. Everson. 1980. Poisonous plants of Utah, USA. Great Basin Naturalist 40: 229-253.
- Edun, Abbas. 2009. Natural Remedies. Bee Culture 137 (6): 55-57.
- Ferris, Clifford D. 1980. Field Notes on 2 Hairstreaks from New Mexico USA with Description of a New Subspecies Lycaenidae. Journal of the Lepidopterists Society 34: 217-223.
- Heil, Kenneth D., Steve L. O’Kane, Linda Mary Reeves, and Arnold Clifford. 2013. Flora of the Four Corners Region: Vascular Plants of the San Juan River Drainage, Arizona, Colorado, New Mexico, and Utah. Monographs in Systematic Botany – Missouri Botanical Garden v. 124.
- Hornig, Ellen. 2008. Marvelous Milkweeds. Horticulture. 105 (6): 50-55.
- Karges, Joann. 2018. From Weed to Wondrous. Natural History. 126 (6): 36-41.
- USDA Soil Conservation Service. 1973. List of Common and Scientific Plant Names for Utah. (Portland, OR: USDA).
- Weakley, A.S. and the Southeastern Flora Team. 2022. Flora of the southeastern United States. University of North Carolina Herbarium, North Carolina Botanical Garden.
- Welsh, Stanley L., Duane N. Atwood, and Joseph R. Murdock. 1978. Kaiparowits Flora. Great Basin Naturalist 38: 125-179.
- Woodson, Robert E. 1954. The North American Species of Asclepias L. Annals of the Missouri Botanical Garden 41: 1-211.