Plant of the Week
Purple Milkweed (Asclepias purpurascens)
By Tania Hanline
A member of the Asclepiadacea family, purple milkweed is found growing primarily in Eastern North America. It is a native perennial listed as endangered in Massachusetts and Wisconsin, and as a species of special concern in Tennessee and Connecticut. Though it is far distributed it rarely grows in large colonies like its common cousin Asclepias syrica. Preferred habitat includes full to part sun on sandy soils of prairies, shrub thickets, shores, and dry open woodlands of such as oak and oak/pine forests. It has also been found growing in wet prairies and calcium rich sites. Research has shown it to have high nutrient requirements.
Purple milkweed has very distinctive flowers whose nectar attracts long-tongued bees, butterflies, hummingbirds, and other pollinators. There are 5 rose pink petals with hoods that are connected at the base below the anther column. The horns are down curved and purplish white. These flower parts are highly modified for insect pollination. Oppositely arranged leaves are pubescent and dark green adaxially and densely pubescent and light green abaxially. Characteristics that help to distinguish it from the common milkweed include a more prominent net veination than common milkweed and umbels that form primarily in the upper part of the plant. Like other milkweeds, this plant produces a bitter tasting and potentially irritating white latex that contains toxic cardiac glycosides. This is the likely reason that this wildflower has few mammalian herbivores other than deer that are believed to negatively impact the dispersal of seeds.
The best time to view this beautiful and special wildflower is from June to August. Current conservation efforts include protecting prairie remnants, maintaining other dry open sites and understanding the natural history that enables it to also exist in moist woods. Population declines are thought to be connected to gene swapping with common milkweed and low levels of flowering.
For More Information
- PLANTS Profile - Asclepias purpurascens, purple milkweed
- USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York. Vol. 3: 26.
- Thomas G. Barnes @ USDA-NRCS PLANTS Database / Barnes, T.G., and S.W. Francis. 2004. Wildflowers and ferns of Kentucky. University Press of Kentucky.