purple milkweed (Asclepias purpurascens)
Asclepias purpurascens L.
CONFIRMATION STATUS: Pending confirmation.
TAXONOMY: The currently accepted scientific name of purple milk-
weed is Asclepias purpurascens L. The flowers of purple milkweed are
quite attractive. This species is less aggressive than Asclepias syriaca
(common milkweed), which it resembles somewhat in appearance. How-
ever, the flowers of purple milkweed are usually a deeper color of purple
and more likely to occur in terminal umbels at the apex of the central stem,
rather than as axillary umbels between the upper leaves. The seedpods of
purple milkweed are smooth, while the seedpods of common milkweed
have soft prickles. Purple milkweed also resembles Asclepias rubra (red
milkweed), but the horns on the flowers of the latter species are straight
and about as tall as the hoods, while the horns of purple milkweed are
shorter than the hoods and curve inward toward the reproductive column
of the flowers.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS:
Habit: This native perennial plant is about 2-3' tall and unbranched. The
central stem is light green, round, and glabrous or slightly pubescent.
Leaves: The opposite leaves are up to 6" long and 3" across. They are
ovate-oblong or broadly lanceolate, with smooth margins that may undu-
late up and down. The leaves often curl upward from the pinkish central
vein. The upper surface of the foliage is mostly glabrous and yellowish
green to dark green (depending on light conditions), while the lower sur-
face is light green and softly pubescent.
Flowers: The central stem terminates with 1-6 umbels of flowers; there
may be a few axillary umbels from some of the upper leaves as well. Each rounded umbel is about 3" across. These flowers have the typical structure
for milkweeds, and can be pale to deep purple in appearance, often with
greenish or rosy tints. However, the central reproductive column and
base of the deflexed petals are white. The hoods are much taller than
the horns; the latter curve inward toward the reproductive column and
appear spike-like (but are thicker toward the base). The flowers have a
Fruit/Seeds: If pollination occurs, the flowers are replaced by seedpods
(follicles) that are held erect and are spindle-shaped. These seedpods are
up to 6" long and 1" across, and tapered on both ends. They have a
smooth surface and are finely pubescent. The seeds have large tufts of
white hair, and are distributed by the wind.
Roots: The root system consists of a fleshy taproot and short rhizomes;
small clumps of plants can be produced vegetatively.
REGENERATION PROCESS: Purple milkweed propogates itself by
reseeding and vegetative reproduction through rhizomes.
HABITAT TYPES: Habitats include moist meadows in woodlands or
near rivers, thickets and woodland borders, bluffs and open woodlands,
oak savannas, glades, and roadsides. This plant usually occurs along
prairie edges near woodland areas, rather than in the open prairie. It
favors somewhat disturbed areas.
SITE CHARACTERISTICS: Purple milkweed prefers is partial sun
and mesic conditions; this plant also tolerates light shade and full sun,
as well as considerable variations in the moisture regime. Immature plants
are inclined to wilt during a drought, and should be watered. The soil can
con- sist of moisture-retaining loam or clay-loam. The plants make rapid
growth during the late spring until they flower and form seedpods, then
they gradually degenerate. It takes 3 years or more for a small transplant
or seedling to reach flowering size. This plant is attacked by the usual milk-
weed insects, including yellow milkweed aphids that are sometimes found
underneath the leaves. The leaves have tendency to turn yellow and curl
in response to dry, sunny conditions, or as they mature.
SEASONAL DEVELOPMENT: The blooming period occurs from late
spring to mid-summer, and lasts about 1-2 months.
GENERAL DISTRIBUTION: Purple milkweed is found through- out
the eastern portion of the United States and Canada, and extends west
through the Great Plains states and provinces. It is generally not found in
the Rocky Mountain states or provinces, the southwest, or the Pacific
Coast states and provinces. It has a limited distribution in the extreme
southeast Atlantic coastal states.
SKY MEADOWS DISTRIBUTION: To be determined.
IMPORTANCE AND USES: The nectar of the flowers attracts long-
tongued bees, butterflies, and skippers. To a lesser extent, green metallic
bees and other Halictid bees may visit the flowers, but they are less ef-
fective at pollination. Another unusual visitor of the flowers is the ruby-
throated hummingbird. Among the butterflies, such visitors as the pipe-
vine swallowtail, giant swallowtail, American painted lady, red admiral,
clouded sulfur, eastern tailed-blue, regal fritillary, great spangled fritillary,
and many others have been reported. The caterpillars of the Danaus
plexippes (monarch butterfly) feed on the foliage. The usual milkweed
beetles and plant bugs are attracted to the foliage, stems, or flowers, as
well. Mammalian herbivores rarely consume this and other milkweeds
because of the bitter-tasting, toxic foliage, which contains cardiac glyco-
sides (see following entry for swamp milkweed for a more comprehen-
sive discussion of importance and uses).
Crooked Run Valley