Partly Parasitic

Piedmont blacksenna (Seymeria pectinata) now grows profusely along the xeric scrub trail at the south Oslo Riverfront Conservation Area (ORCA) near the entrance on Oslo Road just to the east of the Florida Medical Entomology Laboratory. This trail was bush-hogged to widen it last year, and piedmont blacksenna, a native wildflower and root parasite, has replaced the largeflower false rosemary (Conradina grandiflora) and the narrowleaf silkgrass (Pityopsis graminifolia) that once lined this part of the trail.

Also known as comb-leaf blacksenna and comb blacksenna, this annual plant is a hemiparasite (semi-parasite). It can germinate without a host plant, unlike a true parasite, but later is dependent upon a host plant(s) for growth and development.

Piedmont blacksenna parasitizes the roots of neighboring plants robbing them of water and nutrients. Specialized root structures called haustoria are the means by which piedmont blacksenna and many other members of the broomrape family, Orobanchaceae, victimize their neighbors. At ORCA, the piedmont blacksenna appears to be “hooked” into the roots of adjacent scrub oaks and lyonias.

Some young plants are lush and round, having appropriated lots of resources from their neighbors, while other individuals appear to be leggier and less successful. Without attachment to a host plant(s), piedmont senna plants quickly cease to grow and die prematurely.

Its genus name, Seymeria, honors Henry Seymer, a 19th century amateur botanist. Its species name, pectinata, means comb-like and refers to its deeply divided leaves.

Growth sometimes has purplish stems …

Older growth becomes blackened, giving rise to the common name of blacksenna …

Its small, yellow zygomorphic flowers have 5 petals, and the corolla (center) is tinged with red. The flowers and stems are quite hairy. Flowering begins at the bottom of the plant and continues up the stem.

The yellow flowers attract a variety of pollinators especially bees.

Piedmont blacksenna is larval host of common buckeye (Junonia coenia), as is turkey tangle fogfruit (Phyla nodiflora).

In the fall, pollinated flowers turn into a shiny brown capsule that opens to expel about 75 tiny winged seeds which overwinter on the ground. It will be interesting to see if this plant is as prolific next year.