Mystery Plant 672: Devil's Shoestring

It's easy to see this one while speeding down the highway, blooming now, and well into the summer. This is a perennial species, coming back year after year. It likes to grow in groups, and often makes big, crowded patches. Plants produce long, tough roots from a knottly base. The foliage consists of hairy compound leaves arranged alternately (meaning one at a time) up and down the stem. Of course, any compound leaf will bear a number of divisions, and the divisions (or “leaflets”) in this case are lined up on both sides of the midrib (also hairy).

Because the leaflets are lined up this way, we say that the leaf is ”pinnately” compound, like a feather appears, rather than “palmately” compound, wherein the various leaflets are all attached at the same point at the end of the midrib, as in white clover or Virginia-creeper. If you take a close look at  a leaf from our Mystery Plant, you’ll see that there is always a terminal leaflet. All in all, there should be 18-25 or so of these leaflets on one leaf.

One of the neatest things about this species is that its flowers are bicolored. Now, you must remember that at the base of a flower will be sepals, usually green, and above those, there will be (most often) some petals.

Each blossom has five petals arranged in a manner characteristic of many, many members of the bean family, and indeed, our Mystery Plant is placed by botanists into the bean family, or Fabaceae. The uppermost petal of each flower is the largest, and, since it is something like a flag, is sometimes called the "banner." Two smaller, paired petals at the sides of the banner are the "wing" petals, and a second pair of even smaller, twinned petals within the wing petals are called the "keels." Inside the keels hide the 10 stamens and the single pistil, which produces yummy nectar at its base. Some rather romantic botanists have likened this flower shape to that of a butterfly, and have thus come up with the term "papilionaceous" for this floral architecture. If you take a look at the flower while still in bud, it will appear creamy yellow, because of the yellowish banner petal which wraps around the other four. The fully opened corolla, thus, will be attractively bicolored, the banner yellow, and the other petals a deep, rosy pink. Bees like to go after that nectar, and in the process enable pollination.

After the petals fade and fall away, the ovary of the pistil will elongate into a pod, specifically a legume (as you would expect in the bean family) an inch and a half long, or so. At maturity, the pods will split open on 2 seams, releasing the very hard-walled seeds.

This species occurs widely throughout the eastern USA. Including portions of the Great Plains and Texas. It is fairly common along roadsides in dry, sandy woods, and seems to thrive on the driest sands.

 

Answer: "Devil’s shoestring," “Goat’s rue”, Tephrosia virginiana

 

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John Nelson is the retired curator of the A. C. Moore Herbarium at the University of South Carolina in Columbia SC. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or email johnbnelson@sc.rr.com.