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White-stem Milkweed (Asclepias albicans), a Comprehensive Guide in 10 Sections

Introduction

White-stem Milkweed (Asclepias albicans) is a shrubby perennial that is native to southern California and Arizona in the Mojave and Sonoran Deserts. This milkweed is a host plant to two butterflies and two moths and a nectar plant to others. It can be grow to be 3-9 feet tall, but sometimes to 12 feet and is found in dry gravelly areas. The flowers generally flower from March to June, but can flower in other seasons and are greenish to white with hints of brown, pink, or purple, giving them a creamy appearance.

Taxonomy and Naming of White-stem Milkweed (Asclepias albicans)

Herbarium specimen of White-stem Milkweed (Asclepias albicans).
White-stem Milkweed —  Asclepias albicans S.Watson collected in Mexico by The New York Botanical Garden (licensed under CC BY 4.0)
Isotype of White-stem Milkweed (Asclepias albicans).
Isotype — Asclepias albicans S.Watson collected in Mexico
 by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

White-stem Milkweed (Asclepias albicans) was named and described by Soreno Watson, an American botanist, in 1889 in the Proceedings of the American Academy of Arts and Sciences. The description was based on a specimen from Baja Mexico (GBIF). The plant has kept the same name since. This plant is a member of the Dogbane Family (Apocynaceae).

Meaning of the Scientific and Common Names

Scientific Name

The genus name, Asclepias, is named for the Greek god of healing, Asklepios (Flora of Wisconsin). The species name, albicans, means white in Latin and is reference to the color of the stems.

Common Name and Alternative Names

The common name, like the Latin species name, is in reference to the color of the stems. Other names that refer to the stem include whitestem milkweed, without the hyphen. Other names described the leaves and include wax milkweed and wax-leaf milkweed.

Physical Description of White-stem Milkweed (Asclepias albicans)

Plant of White-stem Milkweed (Asclepias albicans).
Plant of White-stem Milkweed —  Asclepias albicans S.Watson observed in United States of America by Diana (licensed under CC BY 4.0)

Description

  • Plant type: Semi-succulent shrub
  • Height: 3 to 12 feet (1-4 m) tall
  • Leaves: A very few 3-whorled or opposite, linear, simple leaves that are lost early, giving the stem a leafless appearance. The leaves can be up to about 1 inch in length.
  • Stem: erect and semi-succulent. The stem does most of the photosynthesis for the plant and is filled with milky sap. It has a waxy appearance giving it a blue-green (Sonoran Desert Naturalist) to white look. Woodson considers this species to be the shrubbiest milkweed (Woodson 1954).
  • Flower color: greenish to white with a brown, pink, or purple tinge. The flower can turn yellowish with age (Felger, et al 2014). The flowers have a star-like appearance.
  • Blooming period: September to June, essentially anytime except the hottest summer months.
  • Fruiting type and period: follicle that hangs from the branch nodes. It soon follows after flowering depending on the flowering time.

Range White-stem Milkweed (Asclepias albicans) in the United States

Range Map of White-stem Milkweed (Asclepias albicans) in the United States.

This species is native to southern California and Arizona in the Mojave and Sonoran deserts. It is also found in the Baja region of Mexico.

Habitat of White-Stem Milkweed (Asclepias albicans)

Mojave Desert in California.
Mojave Desert in southern California — Thomas Farley, CC0, via Wikimedia Commons

White-stem Milkweed grows in dry areas and gravelly slopes that are sparsely vegetated.

Hosted Insects

Monarch butterfly (Danaus plexippus) on a green flower.
Monarch Butterfly on a green flower — U.S. Fish and Wildlife Service, Public domain, via Wikimedia

White-stem Milkweed is a host to the Monarch (Danaus plexippus) and Queen (Danaus gilippus) (Sakai 1993) Butterflies and to the Clio Tiger Moth (Ectypia clio) and another moth (Euchaetes zella).

Other Supported Wildlife

This milkweed, like a lot of other milkweeds, is a nectar source to other species. Insects known to use this plant include orange and black tarantula hawks (a wasp), and small milkweed bugs (Lygaeus kalmi) (Felger et al 2014).

Frequently Asked Questions about White-Stem Milkweed (Asclepias albicans)

What other species are similar to White-stem Milkweed?

White-stem milkweed looks similar to rush milkweed (Asclepias subulata), but the white-stem milkweed is taller and has fewer stems (Felger et al 2014).

Is White-Stem Milkweed toxic?

This milkweed, like other milkweeds, has a milky sap that contains cardenolides that are toxic to humans and animals. The monarch butterfly ingests the toxic sap to make it distasteful to predators.

Gardening with White-stem Milkweed (Asclepias albicans)

Yellow flowers of white-stem milkweed (Asclepias albicans).
Flower of White-Stem Milkweed (Asclepias albicans) — NPS, Public domain, via Wikimedia Commons

Hardiness

White-stem milkweed is hardy in zones 9 to 11. If your garden is within these zones, you can grow it even if you are not within the native range and have the right soil, moisture, and exposure. The monarch butterfly and the Queen butterfly are both wide ranging and are likely to be use the plant outside of it native range.

Optimal Conditions

White-stem milkweed grows best in sandy to rocky soils with a full sun exposure. This plant needs a lot of lateral space since it can spread to 4 feet (Theodore Payne Foundation). It needs to be planted in places where it will not be exposed to frost. In the desert southwest this is generally below 2,500 feet.

References

  • Felger, R.S., S. Rutman, and J. Malusa. 2014. Ajo Peak to Tinajas Altas: Flora of Southwestern Arizona Part 8. Eudicots: Acanthaceae – Apocynaceae. Phytoneuron 85: 1-71.
  • Sakai, Walter H. 1993. Notes on Danaus gilippus strigosus (Nymphalidae: Danainae) in Southern California. Journal of the Lepidopterists Society 47(2): 160-161.
  • Woodson, Robert E. 1954. The North American Species of Asclepias L. Annuals of the Missouri Botanical Garden 41:1-211.
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Robert Coxe

Robert Coxe is a professional ecologist and botanist who has worked as the State Ecologist of Delaware and as an ecologist for the Western Pennsylvania Conservancy. He is also a former Past-President of the Pennsylvania Academy of Science. He currently is an innkeeper at McMullen House Bed & Breakfast LLC and a web designer for Silphium Design LLC.

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