This plant was different and not familiar to the botanists who knew Florida plants well.  The scaly stems stood erect, were pale yellow green and surrounded by small bluish-pink flowers. And try as they might neither Allen Shuey nor Andy Clewell could tease a specimen from the soil with its roots intact.

When the plant was finally identified as cowpea witchweed (Striga gesnerioides (Willdenow) Vatke ex Engler) [stri’ gah jes ner’ ee oy des], agricultural scientists at the state and federal levels were alarmed. Though diminutive, this perky little plant caused entire farms to be abandoned in Africa.

Producing no roots of its own, the cowpea witchweed connects to a legume host. In Africa, it ‘bewitches’ the major crop, cowpeas (Vigna unguiculata), causing up to 100 percent losses in some fields. And this parasite sheds thousands of tiny seeds, so it persists as long as a host crop is cultivated on the soil.

There are 28 species of witchweeds. Except for the cowpea witchweed, the other 27 species attack grasses including sugarcane, maize, millet and sorghum. Some taxonomists place Striga as a member of the Scrophulariaceae, the figwort family; others place it in the Orobanchaceae, the broomrape family.

In Florida, so far, cowpea witchweed has only been found in four counties. Genetic studies show that all of the Florida cowpea witchweeds are closely related, suggesting that the plant was only introduced once. But how is a mystery. And it has always been growing on hairy indigo (Indigofera hirsuta) or alyce clover (Alysicarpus vaginalis); neither of which are vital crops. But there remains the possibility that it may move to other, more vital legumes, so this little plant remains on the Exotic Pest Plant Council watch list.

 

(Compiled from: “Striga (Witchweed), A Photo Gallery of Species”, Parasitic Plant Connection, College of Science, Southern Illinois University, Carbondale, Oct. 2006; “Parasitic Plants as Weeds”, Wageningen Parasitic Weeds Research Group, Wageningen University, no date; “Striga gesnerioides”, Wunderlin, R. P., and B. F. Hansen. 2004. Atlas of Florida Vascular Plants.[S. M. Landry and K. N. Campbell (application development), Florida Center for Community Design and Research.] Institute for Systematic Botany, University of South Florida, Tampa; and “Germination Stimulation of Striga gesnerioides Seeds by Hosts and Nonhosts, D.K. Berner and O.A. Williams, Plant Disease, Vol. 82, No. 11, Journal of the American Phytopathological Society, 1998)