Wild Senna
There’s a yellow-flowered pea family member blooming now, growing as a weed in a neighbor’s garden bed. I was pleased to see it last Sunday afternoon in the shade and with no wind, presenting a perfect opportunity to photograph. Usually, it’s a tough plant to photograph because its just so busy with detail.
The plant is variously known as wild senna, Maryland senna, or American senna. Since 1992 it’s been called Senna marilandica. Before that it was known as Cassia marilandica. Senna you say? That sounds familiar. Where have I seen that name before? Chances are that you read it on the side of a stimulant laxative package.
The commercial source of senna leaves and pods is known as Alexandrian Senna (Senna alexandrina or Cassia senna). The leaves and pods of this Middle Eastern plant has been used as stimulant laxatives since ancient times.
So when early European settlers saw the plant they immediately made use of our native wild senna. They were not the first to use it as a laxative, though. The Cherokee and likely other indigenous groups had used the dried powdered leaves as a strong laxative, for fevers and to treat cramps, though stimulant laxatives are also likely to cause cramps or griping.
Not used today, wild senna, like other stimulant laxatives should really be one of those over-the-counter drugs that should be used under the advice of a healthcare practitioner.
As I stood there photographing the plant, I noticed that no insects were visiting the flowers, yet small ants were scurrying up and down the stem stopping at the base of the leaves. I knew one of the identifying details of this plant species was not just the flowers, leaves, and seedpods, but a distinct clublike gland that sits at the base of the leaf.
The ants were going to this gland, called an extrafloral nectary, and they were licking it like an ice-cream cone. The gland exudes sweet nectar for the ants, and the ants, in turn, feed upon insect predators enemies of the plant so that a single species of bumblebee can visit the flowers, where it must carefully open a closed cap on the anthers to get to the pollen.
Ain’t nature grand? If plants and insects can develop mutually beneficial relationships, maybe there’s an intraspecies lesson there for humans beyond knowledge of laxatives.