Perfect Pods

Perfect Pods
By Anita Carpenter

A lone, 4-foot-tall plant caught my attention as I explored Hartman Creek State Park, Waupaca, Wisconsin. Its shiny, dark green leaves, each 4 inches long, were broadly elliptical, with both ends pointed. The leaves were arranged and attached opposite each other on the main stem. The presence of three ramrod-straight, 5-inch long, upright seed pods was a clue that this plant was a milkweed. Later identified as poke or tall milkweed (Asclepias exaltata) is a plant I don’t encounter very often. It is one of the twelve milkweed species found in Wisconsin.

I was struck by how upright the seed pods were as compared to those of common milkweed (Asclepias syriaca), the milkweed we are most familiar with. Common milkweed pods are somewhat upright but can be pointing in any direction. However, it seems that the pod tip is almost always pointing up even if only slightly. Butterfly milkweed (Asclepias tuberosa) and swamp milkweed (Asclepias incarnata) also produce upright pods.

I started thinking about milkweed pods and realized what a perfect package Mother Nature created for seed dispersal. I gathered a few common milkweed pods for closer study. Each pod has a swollen base that is attached to a small stem that once supported the flower cluster. The small stem is attached to the main stem. Each pod tapers to either a sharp or blunt point at its top end.

In tall milkweed, the flower cluster at the end of the short stem droops. After pollination, the developing pod must turn upright to be in the correct position to facilitate seed dispersal. The shorter flower stem that was once gracefully down-curved is now twisted and resembles a backward letter “S” that supports the upright pod.

When the time is right for seed dispersal, the mature pod of any milkweed splits open, but only on one side. Inside the pod, the tightly packed seeds are arranged like overlapping roof shingles with each seed attached to its own small tuft made up of several fine, soft, white filaments.

Seeds fill the enlarged pod bottom, and the tightly compacted white tufts fill the narrowing top. Carefully open a pod, look inside and then carefully split open, lengthwise, the packaged seeds. You will find the pod core is not a woody stem but tightly packed tufts with one tuft attached to one seed. This is the perfect arrangement for successful and efficient seed dispersal. I found the tufts to be somewhat sticky in an unripened pod.

When the seeds mature, turning from white to brown, the pod dries and starts to split open. Breezes tickle the exposed tufts. The filaments dry and fluff out. Air currents gently catch the soft filaments, lifting the seeds from the pod and sending them on their way to destinations unknown. It may take a few days to empty a pod.

In an unripe pod, the seeds are white. When I opened a pod that was starting to ripen, I was surprised to find a few brown seeds scattered randomly throughout the pod as opposed to ripening from top to bottom.

So, how many seeds are produced in one pod? Using common milkweed pods, I counted seeds in four pods, each randomly picked from four different plants. This is a very small sample size, but the results were: 237, 232, 225, and 225. In this very limited survey, it seems the seed number could be fairly consistent but, as they say, more research is needed.

How do these seed numbers compare to other milkweed species? My “extensive” survey consisted of one pod of butterfly milkweed, whose pod is much slimmer than that of common milkweed. It contained 81 seeds. The seeds were about the same size in both species. And what is the average number of pods per plant per species? One question leads to to another, and I don’t have time for a potential PhD dissertation on this subject.

Autumn is approaching. As a child, I would select an open pod, scoop out the remaining seeds, hold them in my fingertips and let the winds snatch this precious cargo from my grasp. I’d watch the seeds drift skyward. There is something almost spiritual about this yearly ritual, or is it a fleeting return to carefree, childlike wonder?

See Gathering, Cleaning and Sharing Prairie Seed in my blog. I have added one resource: The Ghosts of Evolution  – Nonsensical Fruit, Missing Partners, and Other Excological Anachronisms by Connie Barlow. It is so lighthearted. You will enjoy the read.

The featured image for this blog post (photo that shows on the Home page for this blog post), is common milkweed taken by Tim Lewis, past president of Wild Ones.