Kingdom: Plantae

Phylum: Magnoliophyta -- flowering plants

Class: Magnoliopsida -- dicotyledons

Order: Gentianales

Family: Asclepiadaceae -- milkweed

Common Name: showy milkweed

Species Code: ASSP

Origin: Native to mesic places in western North America from British Columbia to Manitoba and south to Texas.

Rare: no

Form: forb, perennial, erect, 40-120 cm tall, rhizomatous, softly hairy throughout, sap milky.

Mature height: 16-48 inches

Duration: perennial

Longevity: long

Habitat Type: prairie

Wetland Indicator Status: FAC+

Leaves: opposite, petiolate, elliptical to oblong, 10-20 cm long, fleshy, veins conspicuous.

Flowers: perfect, borne in subterminal umbels, pink to reddish purple, fused at the base, parts in 5’s (except the pistil).

Flower color: pink, purple

Bloom: June, July

Bloom starts on: June

Bloom ends on: July

Fruit: follicle, 7-12 cm long, lanceoloid, erect, lanulate, warty; coma long, white; seed flat, ovoid, brown, wing margined.

Characteristics:
It has been proposed to move the genus Asclepias from Asclepiadaceae to Apocynaceae.
Reproduces both sexually by seed and vegetatively by rhizomes.
72,000 seeds/lb (USDA NRCS Plants Database 2009).
x=11 (University of British Columbia 2003).
Insect pollinated (Bookman 1983b).
Bumblebees are the most common pollinator (Finer 2004).
Earlier pollinated flowers are more likely to mature fruits (Bookman 1983b).
97% of ovaries fail to develop into mature pods (Bookman 1983a).
Pods are aborted to favor outcrossing with best pollen donors (Bookman 1984).
High levels of geitonogamy result in high levels of fruit abortion (Finer & Morgan 2003, Finer 2003).
Flowers are perfect.
Native peoples used various plant parts for food and medicine. May be toxic in large quantities.
Fruit is a follicle.
Seeds are dispersed by wind.
Seed down is used by goldfinches in their nests (Craighead et al 1963).
Can be poisonous to livestock.
Larva of the monarch butterfly (Danaus plexippus) are obligate Asclepias feeders (Pyle 2002).
Adults of the western milkweed long-horned beetle (Tetraopes femoratus) feed on the leaves, buds, and flowers of A. speciosa. The larva feed on the roots.

Comments: Plants overwintered outdoors in containers are highly susceptible to winter kill from cold temperatures.

Sun requirement: full

Soil moisture: mesic

Precipitation: 16-30 inches (USDA NRCS PLANTS Database 2009).

Sowing time: fall

Transplant time: spring

Stratification: cold moist

Seed yield: medium

Seed harvest: easy by hand

Seed cleaning: the coma must be removed before the seed can be cleaned.

Planting duration: long

Seed insect problem: none noted

Seed shatter: medium

Seed size: 72,000 seeds/lb (USDA NRCS Plants Database 2009).

Seed harvest date: Sept. to Oct.

Seed comments: Seed should be harvested as the follicle begins to split. Seed is windborne.

Herbaria: Specimen data and digital resources from The Consortium of Pacific Northwest Herbaria

Propagation:
2 protocols in the Native Plant Network:
Pullman WA Plant Materials Center
Corvallis, Oregon Plant Materials Center

Other Propagation Information:
Fresh seeds planted in autumn germinate the following spring and summer (Buhler & Hoffman 1999).
Seeds stored dry at room temperature retained high germination after 60 months. No pretreatment was used (Comes et al 1978).
Reproduces both sexually by seed and vegetatively by rhizomes.

Notes: Asclepias speciosa sometimes has weedy connotations, although probably not deserved. It is an important food for the monarch butterfly larva, which is rare on the Palouse, possibly because milkweed is not common. Can be grown from seed. It does spread by rhizomes and is probably too aggressive for a small garden. Should be better in a more wild setting (Skinner et al 2005).

References:
Bookman, Susan S. 1981. The Floral Morphology of Asclepias speciosa (Asclepiadaceae) in Relation to Pollination and a Clarification in Terminology for the Genus. American Journal of Botany 68:675-679.

Bookman, Susan S. 1983a. Costs and Benefits of Flower Abscission and Fruit Abortion in Asclepias speciosa. Ecology 64:264-273.

Bookman, Susan S. 1983b. Effects of Pollination Timing on Fruiting in Asclepias speciosa Torr. (Asclepiadaceae). American Journal of Botany. 70:897-905.

Bookman, Susan S. 1984. Evidence for Selective Fruit Production in Asclepias. Evolution 38:72-86.

Buhler, Douglas D., and Melinda L. Hoffman. 1999. Andersen's Guide to Practical Methods of Propagating Weeds and Other Plants. Weed Science Society of America. Lawrence, Kansas. 248 pp.

Craighead, John J., Frank C. Craighead, and Ray J. Davis. 1963. A Field Guide to Rocky Mountain Wildflowers. Houghton Mifflin Co. Boston, MA.

Finer, Matt, and Martin Morgan. 2002. Effects of Habitat Fragmentation on Plant-Pollinator Interactions. Abstract of a presentation at the 2002 Ecological Society of America 2002 Annual Meeting. Online at http://abstracts.co.allenpress.com/pweb/esa2002/document/?ID=6094

Finer, Matt. 2004. Insight into the Pollination Crisis: Effects of Population Size on Pollinator Diversity for Showy Milkweed. Douglasia 28(4):7-8.

Finer, Matthew. 2003. Effects of Geitonogamy, Habitat Fragmentation, and Population Size on Plant Reproductive Success: Ecological and Evolutionary Studies. PhD thesis, Washington State University (Biological Sciences).

Finer, Matthew S., and Martin T. Morgan. 2003. Effects of Natural Rates of Geitonogamy on Fruit Set in Ascepias speciosa (Apocynaceae): Evidence Favoring the Plant's Dilemma. American Journal of Botany 90:1746-1750.

Pyle, Robert M. 2002. The Butterflies of Cascadia. The Seattle Audubon Society, Seattle, Washington. 420 pp.

Skinner, David M., Paul Warnick, Bill French, and Mary Fauci. 2005. More Palouse Forbs for Landscaping. Online at http://www.wsu.edu/pmc_nrcs/Docs/More_Forbs_for_Landscaping.pdf

USDA NRCS. 2009. The PLANTS Database (http://plants.usda.gov, 23 July 2009). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

University of British Columbia. 2003. British Columbia Flora. University of British Columbia Botanical Garden and Centre for Plant Research. Online at http://www.bcflora.org/ Accessed 1/1/06.

Links:
Plant Guide from the USDA PLANTS Database
Species information from the University of Washington Herbarium