at my touch sensitive
leaves fold along the midline --
sleeping partridge pea
As a child I loved touching the feathery leaves of sensitive partridge pea to watch them fold together like the wings of a butterfly. The compound leaves also fold up at night, which gives the plant another of its many common names, sleeping pea. In fact, the leaves look a lot like mimosa leaves, another sensitive plant.
On the day the temperature hits 100 F (38 C), the delicate-looking plants are growing along the shoulder of the shady hill west of our little bridge. Large-flowered sensitive pea seems to like a mixture of a little shade with a little sun, and doesn't mind growing right in the gravel.
This annual native legume has a lot going for it. It reseeds easily and grows quickly on disturbed ground, helping to stop erosion, while the little nodules on its roots produce nitrogen, nourishing the plant and improving the soil. It's also a sensitive neighbor. Once other plants begin to grow in the area, the partridge pea, with a life-span of about two years, slowly gives way.
The pea-like flowers have developed an interesting pollination strategy. Each bright yellow blossom has five petals, with the lowest one being the largest, like an inviting landing platform. The job of one of the side petals is to curve over the purple pollen-containing stamens, encouraging "buzz pollination" by long-tongued bumblebees and honeybees. Attracted by the nectar and perhaps guided by the red spots at the center of the blossom, these bees are able to buzz their way under the petal guard and lap up the nectar, while getting dusted with pollen.
The flowers keep blooming until the first frost. It is such a good source of nectar when other flowers are not blooming that beekeepers often plant partridge pea for honey production. Of course, they probably don't label their honey "Locust Weed," one of the plant's other names. But "Golden Cassia" sounds enchanting. The Latin name for the plant is Chamaecrista fasciculata, but it used to be classified as Cassia chamaecrista.
In addition to the leaf-folding trick, partridge pea has another clever defense strategy. It produces nectar from orange glands at the base of the leaves, which attract butterflies, ants, flies, wasps and sweat bees. it is thought that the visiting ants remove insect pests from the plant.
When the long, narrow seed pods are ripe, they split open and spiral to eject the seeds, as far as a meter. Those seeds are a nutritious source of food all winter for partridge, which is how it gets the name partridge pea, as well as quail, pheasant, wild turkey, other grassland birds, field mice, rabbits and deer. The close-growing plants also create shelter for ground birds. Both the seeds and the leaves contain a cathartic substance which is toxic for grazing animals if eaten in large quantities, though whitetail deer appear to eat the plant with impunity.
Another name for this native member of the pea family is prairie senna, because it has some of the same laxative characteristics. Various native peoples used the plant medicinally, for such conditions as nausea, urinary tract problems, sore throats, skin problems, a stimulant, fevers, infections and malaria. Probably better for those of us who are not trained in traditional medicinal herbs to just admire the cheery yellow flowers and have fun touching the sensitive leaves.