Sunday, June 03, 2007

"Ah...perennis."


There's a glaring omission in Edgar Denison's glossy Missouri Wildflowers and Caroline Dorman's landmark Wildflowers of the Deep South. Neither book includes swamp milkweed in their catalogues of native plants. Asclepias perennis is one of the more delicate, pink-flowering milkweeds and it's only found in the soils of the Mississippi embayment.

I have a colleague who, earlier in his career, worked on embayment-specific dragonflies in southern Illinois. He has a special place in his heart for the embayment and one of the most common plants in it, A. perennis. So, last week, when I mentioned to him that milkweed is in full bloom in the swamp, he turned wistful and sighed, "ah, Asclepias perennis. Is there a finer one around?" That's a personal question. Glade lovers think the same about A. verticillata, a conservative green flowering milkweed that only grows on dolomitic south facing slopes. Prairie aficionados appreciate the bright orange A. tuberosa above all others because it stands out in the prairie every summer. Regardless, why is the swamp species left out of wildflower guides? A. perennis is like a lot of other embayment-only plants: it's only known from a few states, from a dwindling and maligned (but ecologically rich) habitat.

Ask a monarch butterfly which is the finest of the milkweeds and the rating system falls apart. Monarchs depend on any plants of the genus Asclepias for egg laying. The larval form of monarchs eat milkweed leaves and stems, even of the popular cultivar, A. currasavica from Brazil, sold in nurseries as "butterfly weed." Monarch numbers continue to drop worldwide not only because of habitat destruction in their wintering grounds, but habitat destruction in America. Many common milkweeds thrive in overgrown, weedy patches, areas that are regularly mowed for highway maintenance or, worse still, sprayed with herbicide.

Long before perennis was blooming this spring, monarchs were hovering around a concentrated area in the swamp. I didn't notice the milkweed growing there among the sedges, but the monarchs did. They have the ability to see things we can't. They knew perennis was there months before it was in bloom. Of course, now that it's in full bloom I can barely take a picture of the plant without a butterfly on it.

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