What makes a milkweed?
Milky sap, for one thing, which all milkweeds except butterfly-weed have. Flowers, for another. Large or small, white or green or pink or purple or orange, in dense clusters or on droopy umbels (short flower stalks from a common point like umbrella spokes), all milkweed flowers have parts in fives. Five “hoods” form the upper part of each flower, surrounded by five petals that curve down and away. No other flower we’ve ever seen looks quite like the elegant structure of a milkweed flower. The flowers eventually form long seed pods that ripen and burst, the seeds riding the wind on silky tufts that some birds use to line their nests.
Bumblebees, wasps, and butterflies are milkweed’s main pollinators, but other insects use milkweed for food for themselves and their larvae. For monarch butterflies, though, milkweed is essential–the only plant upon which they lay their eggs. No milkweeds, no monarchs.
It’s a thrill to find the small white monarch eggs looking like half a very tiny football on the undersides of milkweed leaves, an even greater thrill to find (or even hear) the hatched caterpillars munching on the leaves. The best thrill of all: watching a caterpillar contort itself into an elegant chrysalis and, days later, hatch out as a butterfly and fly away. Which will only happen as long as we have milkweeds.
Minnesota is home to fourteen species of milkweed, although three of Minnesota’s milkweed species are threatened, one is endangered, and one, purple milkweed, may be extirpated (no longer found in the state). We’ve crossed into Iowa to see prairie milkweed (before we finally found it after much searching here in Minnesota), and we plan to head to Wisconsin next summer to look for purple milkweed, which still grows there. Rare or common, short or tall, in prairie or woods or along lakes and creeks, milkweed’s lovely and distinctive flowers make them a stand-out wherever we find them.
Common milkweed (Asclepias syriaca)
Common milkweed has showy clusters of pink flowers and wide oval leaves with soft hairs on the undersides. Flowers ripen into bumpy seedpods that open to release seeds on silky parachutes that ride the prairie wind. Like other milkweeds, this is a plant that monarchs lay their eggs on and that their larvae eat until they are ready to metamorphose into butterflies. If you find a large green-and-black-striped caterpillar-looking larva on a milkweed, listen closely. You might hear it chomping its way through a leaf on its way to becoming a butterfly. Common milkweed grows two to five feet tall and blooms June to August. We once came upon a colony of common milkweed in bloom on a hot day, and their sweet scent rolled over us through the humid air.
Sullivant’s milkweed (Asclepias sullivantii)
Sullivant’s milkweed has clusters of pink flowers with five downward-pointing petals and five pink hoods over them. One way we’ve learned to help distinguish this milkweed from common milkweed is to look closely at the leaves: Sullivant’s leaves are more vertical than common milkweed’s and feel smooth and waxy rather than fuzzy underneath. Sullivant’s is said to resemble purple milkweed as well as common milkweed, but since purple milkweed hasn’t been seen in Minnesota for at least 125 years, there’s not much chance of confusion. This state-threatened milkweed, an indication of less-disturbed prairie, grows two to three feet tall and blooms from June to August.
Swamp milkweed (Asclepias incarnata)
This is another unmistakable milkweed with its deep reddish-purple flowers and narrow leaves and its preference for wetter places. We’ve seen swamp milkweed crowded with monarch caterpillars, sometimes three to a leaf and thirteen or more on a single plant, but hummingbirds along with bees and other pollinators also visit swamp milkweed. It grows one for four feet tall and blooms from June to September.
Showy milkweed (Asclepias speciosa)
We’ve had the most luck spotting this showstopper of a milkweed alongside roads and highway. One hot fourth of July at Schaeffer prairie we interrogated what felt like a million milkweeds in search of a showy milkweed, only to spot one later that alongside a road by Regal meadow, a Nature Conservancy site, and we’ve seen it since along several other highways. It’s hard to mistake its showy flowers for anything else. The petals have long horned hoods, light pink against the bright pink sepals, making the flowers look like clusters of tiny stars or a Chihuly glass sculpture. Showy milkweed grows 2 to 3 feet tall, blooms from June to August, and definitely lives up to its name.
Green Milkweed (Asclepias viridiflora)
When we first saw green milkweed we ecstatically misidentified it as narrow-leaved milkweed because of the narrow leaves, then learned our mistake, since narrow-leaved milkweed only grows in one known location in the state—which was not the location we were at. Green milkweed’s leaves are still narrow, (although not as narrow as narrow-leaved milkweed) and mostly opposite each other on hairy stems. The few dense clusters of pale green flowers grow in the leaf axils. The shape of the leaf can vary from plant to plant. Long narrow leaves, less than an inch wide, have smooth edges; Shorter, wider leaves up to 2 1/2 inches wide often have curly edges. Because everything about this milkweed is green and because it only grows 1 to 3 feet tall (the ones we’ve seen are usually on the short side), it’s easy to overlook at first. It’s a sweet find in a dry prairie, where it blooms from June to August.
Narrow-leaved milkweed (Asclepias stenophylla)
Narrow-leaved milkweed is listed as endangered in Minnesota and only grows in one know location. We were ecstatic to think we’d seen it growing on a gravelly hillside, then learned that we’d mistaken green milkweed’s narrow leaves for even narrower leaves of narrow-leaved milkweed. While narrow-leaved milkweed does grow on hillsides, we had the wrong hillside in the wrong part of the state. Eventually we made our way to the right hillside, and once we spotted narrow-leaved milkweed the difference was obvious. The plant’s long, widely spaces leaves are only about ¼ inch wide. Round clusters of pale flowers grow in the leaf axils close to the top of the plant. Narrow-leaved milkweed grows 1 to 2 feet tall and blooms from June to August, but it can be found even when it’s not blooming (we did) as long as you are unafraid to scale a very steep goat prairie. Very steep. But worth it.
Clasping milkweed (Asclepias amplexicaulis)
Clasping milkweed made us laugh when we found it—if we hadn’t known what we were looking for, we might never have identified it as a milkweed. The plant looks (to us) like a cross between a vintage light fixture and a space alien. Clasping milkweed is a threatened species in Minnesota and grows 2 to 3 feet tall. Long, wide, wavy leaves clasp the lower part of the stem, which may account for its common name. A tall, unleafed stem ends in a single cluster of widely spaced pinkish flowers that bloom in June and July. It likes uncrowded space and only grows in upland prairies and dry savannahs, which is where we found it thanks to directions from a friend in the know.
Prairie milkweed (Asclepias hirtella)
This is a threatened species in Minnesota, growing in only one known location in Minnesota. Before we found it there, we crossed the border into Iowa to a prairie where prairie milkweed also grows. It’s an unobtrusive milkweed, one to three feet tall with clusters of greenish purple flowers that bloom in the leaf axils in June and July. Narrow, alternate leaves crowd the stem. When we finally tracked prairie milkweed down in its Minnesota location we were ecstatic to find more than fifty plants in lovely and delicate bloom.
Whorled milkweed (Asclepias verticillata)
It’s hard to remember that this is a milkweed when we first see it. The pale flowers are small, and the narrow leaves whorl around the stem unlike other Minnesota milkweed. It’s also a late bloomer, spreading its lacy cheer and offering monarchs a food source from July to September. Plants grow one to two feet tall and spread by both seeds and rhizomes, which means if you see one whorled milkweed, you’ll probably be standing among a whole delicate-looking sweep of them.
Woolly milkweed (Asclepias lanuginose)
Woolly is an apt name for this milkweed. The stems are densely hairy, and leaves have fine hairs top and bottom. Pale flowers bloom in June and July in a single cluster at the top of the stem. The plant itself is only a foot high at most. We were lucky to find it in a sandy prairie following the directions of a knowledgeable friend, and even then we looked hard before we spied it down in the prairie grasses.
Oval leaf milkweed (Asclepias ovalifolia)
Short among milkweeds, growing no more than two feet high, oval-leaf milkweed is also known as dwarf milkweed. We first saw it growing along the steps down to a beach in part shade, and it is mainly a denizen of sandy habitats, including prairies, roadsides, and oak savannas. A cluster of pale flowers at the top of the stem blooms in June and July.
Poke milkweed (Asclepias exaltata)
One of our taller milkweeds, poke milkweed can grow 3 to 5 feet tall and blooms from June to August. Pale flowers bloom in droopy, open clusters. The leaves are oval-shaped, but the plant’s size and sparse-looking flower clusters make it easy to distinguish from oval-leaved milkweed. It grows in shade or part shade at the edges of woods.
Butterfly-weed (Asclepias tuberosa)
Butterfly-weed is easy to spot on the summer prairie even though it only grows one to two feet tall—its flowers range from pale yellow orange all the way to deep red. Leaves are long and narrow, and multiple stems can give it a bushy appearance. It blooms from June to September, providing food for monarchs and other butterflies and pollinators. Butterfly-weed is the only milkweed that has clear sap instead of milky sap. Who knows why? Not us.
Purple milkweed (Asclepias purpurascens)
True to its name, this milkweed has purple flowers. Sadly, it hasn’t been recorded in Minnesota in 125 years, so although we’ve looked hard, we haven’t found it. Its bloom time is June and July, and it grows 2 to 3 feet tall. Flower clusters grow in axils where the leaf meets the stem and also at the top of the stem. Leaves are long and wide. We still live in hope of seeing it, possibly in Wisconsin where it still grows but is listed as endangered.
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