Description: This
native perennial plant is 1½–2' tall and unbranched. The central
stem is light green and usually slightly pubescent, otherwise it is glabrous.
The leaves are usually opposite and angle strongly upward from the stem,
otherwise they are alternate. They are up to 5" long and 1¾" across, and
are usually lanceolate with short petioles. Because this is a variable species,
the leaves can assume other forms as well. A typical leaf has a prominent
central vein and smooth margins that gently undulate up and down. It is often
slightly pubescent, otherwise glabrous. A single umbel of flowers may appear
from the axils of the upper pairs of leaves. A typical plant will have 1-3
umbels, with each umbel consisting of 15-30 flowers. Each umbel has a short
stalk and hangs downward. Each flower is about 1/3" long, consisting of 5 upper
hoods and 5 deflexed petals. The hoods are without horns, and the central
reproductive column is very short or absent. Instead, there are masses of
winged pollinia. The flowers are light green to green, becoming yellowish green
or purplish green as they age. Their pedicels are about ½" long and
hairy. The blooming period occurs during early summer and lasts about 3 weeks.
If successful cross-pollination occurs, a flower will be replaced by a
spindle-shaped follicle about 5" long and 1" across at its widest. The surface
of a follicle is smooth, but usually slightly pubescent. This splits open along
one side, and releases numerous seeds, each one with a large tuft of white
hair. Seed distribution is by wind. The root system consists of a central
taproot. This plant occurs as widely scattered individuals, and rarely forms
colonies.
Cultivation: The
preference is full sun and rather dry conditions. This plant will also tolerate
partial sun and mesic conditions. If anything, poor sterile soil is preferred,
containing gravelly or sandy material, as this reduces competition from taller,
more aggressive plants. However, it will also grow quite well in rich loam.
After it blooms and forms seedpods, this plant steadily
deteriorates.
Range & Habitat:
Short Green Milkweed is widely distributed in Illinois, but is absent from some
eastern and central counties. In areas where it occurs, Short Green Milkweed is
an occasional plant. Habitats
include openings in
upland forests that are rocky or sandy; mesic to dry black soil prairies, sand
prairies, gravel prairies, and hill prairies; barrens, limestone glades, and
sand dunes; and abandoned fields. This species of milkweed usually occurs in
high quality habitats, rather than disturbed areas. It is easy to overlook,
even when it is in bloom.
Faunal
Associations: The nectar of the flowers attracts bumblebees and
other long-tongued bees, which are the principle pollinators. Ants are also
attracted to the nectar, but they are not effective pollinators. The foliage
and other parts of the plant are consumed by the larvae of Danaus
plexippes (Monarch Butterfly) and the usual assortment of milkweed insects
(see Insect Table). Mammalian
herbivores shun this plant because the white latex of the leaves is toxic and
provides the foliage with a bitter taste. The white latex also clogs up the
mouthparts of insects, reducing the number of species that can feed on this
plant.
Photographic Location: The
photograph was taken at the Paxton Cemetery Prairie in Ford County, Illinois.
This plant was growing in a mesic black soil prairie.
Comments: This non-showy plant is unlikely to
receive favor from the mass market in horticulture, but it is nonetheless quite
interesting to examine. This milkweed species is rather variable across
different localities; there is a variety with narrow leaves that occurs in
sandy areas near Lake Michigan. Short Green Milkweed can be distinguished from
most other species of milkweeds by its nodding umbels of green flowers. The
rare Asclepias meadii (Mead's Milkweed) has this characteristic, but its
flowers are noticeably larger in size, and the hoods of its flowers have horns.
Another milkweed species, Asclepias hirtella (Tall Green Milkweed)
produces nodding umbels of flowers, but they are usually more white than green
in appearance, and its leaves are more linear and narrow than the leaves of
Short Green Milkweed.