Primarily a Coastal Plain plant that thrives in ditches and wet, disturbed areas, Bagpod – Sesbania vesicaria – is a relative newcomer to the Falls Lake area. Populations of this tall, gangly, woody annual have gradually been moving inland and northward, establishing colonies in a few places along the shoreline of Falls Lake and even appearing along a small suburban greenway.
Individual plants can be quite large, up to 12 feet high, and have a stark, skeletal appearance.
Bagpods are legumes, members of the bean family (Fabaceae), whose common name results from the large, dangling pods that usually contain 2 seeds each. Mature pods have two distinct layers protecting the seeds. A tough outer layer protects a thin, flexible inner layer that contains the seeds. The inner layer looks a lot like a soft, pale sock and can easily be removed from the outer layer.
The following, closer view shows the soft, inner layer inside the tough, outer layer. The shadow of the seed can be seen in the top chamber of the inner layer.
The soft, inner layer of the pod can be easily removed from the outer layer.
A few years ago, I picked and planted 7 seeds from a dry Bagpod plant in early winter, not knowing at that time what the plant was. No seeds germinated the following spring, but a year after that, in early April, 3 out of the 7 seeds germinated.
Sesbania vesicaria seedlings have a fascinating early development. The cotyledon leaves are smooth and thick, and are rectangular with rounded ends, like an oar. The first true leaf is also smooth and thick, but a little larger and more ovate. The second true leaf, which comes in opposite the first, is a compound leaf with the leaflets opposite each other. This compound leaf pattern is sometimes called even pinnately compound. Each new leaf after that is alternate and compound, with 8 to 40 opposing leaflets.
Flowers appear in the leaf axils in mid-summer to early fall and are yellow , but can be tinged with red or orange. So far, the flowers in the Falls Lake area have been yellow and not tinged with other colors.
On the South Carolina Coastal Plain, Sesbania vesicaria can occur in huge numbers. In the summer and fall, the ditches of the Bear Island and Donnelley Wildlife Management Areas are full of large numbers of these plants, stretching for miles. They are sometimes found mixed with populations of Sesbania herbacea, a similar plant whose seed pods are long, thin and curving.