FIELD NOTES: Milkweeds
~by Jim Eagleman
Each early summer milkweeds make a grand display near my home, filling abandoned fields and roadsides with dense clusters of yet-to-open, pinkish-purple flowers. Gazing out over rolling terrain, I see many individual patches containing dozens of soon-to-be mature milkweed plants. Some newly purchased native milkweed rootstocks for our natural area are slow to mature, but soon more young starts will appear. This growth pattern occurs because the perennial milkweed propagates by means of an underground root called a rhizome. Extending in all directions, the rhizome sends up a multitude of flowering stalks. Each colony of milkweeds in a field or garden may actually be a single clone of plants growing from a common root system.
Common milkweed, one of many genera, has a range from southwestern US deserts to the Rockies and across the east. Found in fields, waste areas, and roadsides, they don’t seem to have a preference where they grow. The milkweed genus, Asclipias comprises nearly 100 species and most are native to North and South America.
The name Asclepias comes from Asklepios, the Greek god of medicine. He is usually depicted carrying a staff intertwined with a snake, the modern day symbol of medicine. So it comes as no surprise milkweeds have been used for a wide variety of ailments, experimentally, including asthma, dysentery, heart disease, stomachaches, snakebites, ringworm, warts, tapeworms, and even syphilis. Its popularity as a medicine may be related to the supply of a bitter, milky latex produced in a special system of tubes that branch throughout the plant.
The latex contains a substance identified as a cardiac glycoside. In small doses it can cause nausea and vomiting. In larger doses, as a poison to vertebrates. For the plant, the latex acts as a defense, visible when a leaf stem is pinched and the white liquid oozes out. When exposed to air it quickly dries and becomes sticky, gumming up the mandibles (mouthparts) of insects. Very few insects can tolerate the latex from milkweeds, but several are specialized feeders on the plant, eating nothing else. These specialists, like the monarch caterpillar, have evolved a means of coping with the plant’s toxin. They don’t deactivate it but incorporate it into their blood, permeating every portion of their body. This makes them distasteful to predators like blue jays, since the food they eat is poisonous.
Of the 15 or so species of milkweed native to Indiana, most are found in open areas. A few are found in forested communities not densely shaded. The common purple milkweed is found more in open woodlands. Poke, variegated, whorled, and thinleafed milkweeds are also found in Indiana forested environments. I’m always on the lookout for these plants with a flower color unlike the solid dark red or purple color of the common. Another milkweed is the beautiful butterfly weed we see blooming along county roads. Its showy orange flowers are a standout, one of only a few to have this color, and the only milkweed with alternate leaves and colorless juice.
My milkweeds occupy several places in our recent hugel mounds created to improve soil. Their broad, usually paddle-shaped leaves make them easy to spot among other green plants struggling for sun and space. Now that cicada emergence is over, we’ll watch for another natural drama, the arriving pollinators as milkweed comes into bloom. It’s the monarch butterfly we know as chief pollinator but other insects will arrive, attracted to the fragrant scent, and rewarded with a meal of nectar. These include, but not limited to, bumble bees, yellowjackets, skippers, several species of moths, and the hummingbirds.
Later into fall, the feathery seeds of milkweed will take flight, a plume of fluff, lofting seeds like tiny parachutes. Tightly wrapped in a pointed husk about 3” in length, the spirally arranged seeds inside resemble a pine cone and gently fall out as the cone splits open and dries. The “silk” can be found in a variety of bird nest construction, including goldfinch and buntings.
One natural event gives way to another. It’s a schedule I track on the summer calendar as friends tell me what they see in their woods. It’s all part of the natural sequence, predictable and anticipated. Undeterred by COVID, nature reassures. It wasn’t interrupted and it certainly never disappoints. I am heartened and anxious as our lives slowly return to normal, and I’ll look for the milkweeds to grace our fields and gardens for yet another year.