Weeds of Wednesday: Coffee Senna

The devil, often, is in the detail …

When a new plant volunteered in our yard after Hurricane Irma, I did not look too hard at it and thought, happily, that privet senna (Senna ligustrina) had volunteered.  The Florida Plant Atlas calls it privet wild sensitive plant, and its even pinnate leaflets are shown above.  This native plant grows at the Oslo Riverfront Conservation Area (ORCA) in disturbed areas and along hammock edges.  It is the larval host plant for the cloudless sulphur (Phoebis sennae), sleepy orange (Eureka nicippi), and orange-barred sulphur (Phoebis philea) butterflies.

As it grew, the “volunteer” in our yard, shown above, began to look a bit different and turn out to be septicweed (Senna occidentalis).  This non-native annual (or biennial) is naturalized throughout Florida and the southeast U.S. — not to mention Australia and  eastern Africa — and grows very swiftly.   Already, it has flowered and produced long, erect flat brown pods.

Each legume (pod) contains many hard black seeds, which sometimes are ground and brewed into a coffee-like beverage, giving rise to the common name coffee senna.

Compare & Contrast …

The native privet senna has narrower lanceolate leaflets, often has more paired leaflets (6-8), and has distinctively yellow leaf margins, shown below …

Septicweed, by contrast, has more obovate (egg-shaped) leaflets, less paired leaflets (3 – 6), and often darkened leafstems (rachis), as seen in the seedling below …

At least the “volunteer” was not Christmas cassia (Senna pendula var. glabrata), which is categorized as category #1 invasive pest plant by the Florida Exotic Pest Plant Council.  Climbing senna, climbing cassia and Christmas cassia are other common names for this plant.  The Florida Plant Atlas calls is Valamuerto.

Both native privet senna and the non-native septic weed have an erect growth habit.  Christmas senna, left to its own devices, sprawls over other foliage …

Its large cylindrical pods are pendulous, ripen from green to pale brown, and often have irregular constrictions.  This fast-growing, short-lived nasty invasive is still sold in the landscape trade and, for awhile, was mistakenly planted at the Audubon House as seen in an old photo below fruiting …

Note that its leaflets have a rounded tips (obtuse apices), and its showy flowers are bright yellow with 3 prominent curved stamens.

Details matter!