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Scientific Name
Subfamily Asclepiadoideae
Family
Apocynaceae (dogbanes); formerly Asclepiadaceae (milkweeds)
Description
In Missouri, milkweeds are perennial herbs or twining vines. Most have white latex (milky sap), but some have clear sap. Leaves are simple, most commonly opposite; blades variously shaped but often somewhat wavy. The unique, 5-parted flowers grow in rounded clusters (umbels). The 5 calyx lobes are spreading or reflexed. The 5 corolla lobes are spreading, reflexed, or erect. In the center of the flower, the stigmas and anthers are fused into a 5-lobed or angled headlike structure called a gynostegium. Surrounding the gynostegium is a 5-parted corona (crown) of variously shaped petal-like structures that can resemble hoods or horns. Pollen is contained in pairs of tiny sacs called pollinia; these entire sacs are used in pollination. There are 2 separate pistils per flower, below the gynostegium. Each pistil has a single chamber. The fruits (follicles) are podlike, sometimes growing in pairs. Each fruit contains numerous seeds, which are usually flattened and have a tuft of long, silky hairs at the tip.
Size
Varies with species. Some are stout plants 3 feet high, some are vines with long twining stems, etc.
Where To Find
There are 22 species in 4 genera of milkweeds in Missouri: Asclepias (milkweeds; 17 species), Cynanchum (2 species; sand vine is the most common), Gonolobus (angle-pod; 1 species), and Matelea (climbing milkweeds; 2 species).
Habitat and Conservation
Many of Missouri’s milkweeds are weedy and grow in open, disturbed soils, such as roadsides, pastures, and agricultural areas. Others are associated with high-quality native habitats such as prairies. The increasing use of herbicides has drastically reduced agricultural and roadside weeds, including milkweeds. This is a problem for the monarch butterfly, which requires milkweeds as larval host plants. Monarch numbers have been plummeting in large part due to the dramatic reduction of milkweeds.
Status
The entire former milkweed family (Asclepiadaceae) has recently been rolled into the dogbane family (Apocynaceae). Botanists have long known the two families were closely related. In about 2000, they announced that DNA evidence showed they were so close genetically that calling them separate families was not warranted. The milkweed group, with its distinctive floral structures, is yet considered a unique subfamily or tribe of the dogbane family.
Life Cycle
Life Cycle
A milkweed plant has many flowers, but relatively few fruits develop. Their unusual pollination biology, which promotes outcrossing, causes this. To be pollinated, a milkweed flower must be visited, first, by one insect pollinator, whose leg enters a slot in the flower and removes a pollen-bearing structure. Then it flies away with it stuck on its leg, perhaps to pollinate another milkweed. Meanwhile, the original milkweed flower waits for another insect to bring pollen from another milkweed.
Human Connections
Milkweeds have a long list of historical medicinal uses, and the milky latex was once explored as a potential source of rubber. The silky floss of the seedpods has been used for stuffing pillows and life preservers. Today, people are planting milkweeds to help monarch butterflies survive.
Ecosystem Connections
Many bees, butterflies, and skippers drink nectar from the flowers, and crab spiders often hide in the clusters, hunting them. Monarch butterflies use milkweeds as larval food plants, collecting the sap’s toxic cardiac gycosides in their bodies and becoming unpalatable to predators.
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This cluster of whorled milkweed blossoms exemplifies the unique look of milkweed flowers, recognizable at a glance.
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Prairie milkweed, like most other milkweeds, bears pods holding numerous seeds, each with a parachute of silky hairs.
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Credit
MDC Staff
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Credit
Chris Evans, Illinois Wildlife Action Plan, Bugwood.org
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A close look at the individual flowers of butterfly weed shows they have the same unique structure as other milkweeds.
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David Stonner
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One of our earliest blooming milkweeds, fourleaf milkweed bears round clusters of pink or cream-colored flowers.
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Anonymous
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Swamp milkweed’s flower clusters form at the tops of the stems.
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Rob Routledge, Sault College, Bugwood.org
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Swamp milkweed bears paired, 4-inch, slender pods that are smooth but usually slightly hairy.
Credit
Catherine Herms, Ohio State University, Bugwood.org
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Beloved by bees, butterflies, and other insects for its nectar, sand vine is also a problem weed that can be difficult to eradicate.
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Sand vine is a native milkweed vine that provides needed nectar for monarch butterflies as they migrate southward in late summer.
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The brown, starlike, spreading flowers of climbing milkweed differ from those of other milkweeds.
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Mark Sullivan
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Butterfly weed, a type of milkweed, is a favorite nectar plant for butterflies, and the leaves are eaten by the caterpillars of monarchs. One of our showiest native wildflowers, butterfly weed is also a favorite of gardeners.
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David Stonner
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MDC Staff
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Credit
Jim Rathert
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The great spangled fritillary is common and easily recognized. This glorious butterfly is often seen in city yards and gardens as it seeks flowers.
Credit
Donna Brunet
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Where to See Species
About Wildflowers, Grasses and Other Nonwoody Plants in Missouri
A very simple way of thinking about the green world is to divide the vascular plants into two groups: woody and nonwoody (or herbaceous). But this is an artificial division; many plant families include some species that are woody and some that are not. The diversity of nonwoody vascular plants is staggering! Think of all the ferns, grasses, sedges, lilies, peas, sunflowers, nightshades, milkweeds, mustards, mints, and mallows — weeds and wildflowers — and many more!