About Stachytarpheta cayennensis (Rich.) Vahl
Stachytarpheta cayennensis is a flowering plant species belonging to the verbena family. It has many English common names: blue snakeweed, Cayenne snakeweed, dark-blue snakeweed, bluetop, nettle-leaf porterweed, rattail, rough-leaf false vervain, blue rat's tail, Brazilian tea, Cayenne vervain, false verbena, joee, nettleleaf velvetberry, and Cayenne porterweed. It also has common names in other languages: honagasō in Japanese, gervão-urticante in Brazilian Portuguese, piche de gato and rabo de zorro in Spanish, herbe à chenille, herbe bleue, and queue de rat in French, ōi or ōwī in Hawaiian, sakura or ouchung in Chuukese, and tiāki in Māori.
This species is native to the Americas, ranging from Mexico south through Central and South America to Argentina, as well as many Caribbean islands. It is an introduced species in many other regions around the world, including parts of Africa, India, Indonesia, Australia, Florida in the United States, and many Pacific Islands. Its current distribution is considered pantropical, and it has become an invasive species in many places such as New Caledonia.
This plant is a perennial herb or shrub that can grow up to 2 to 2.5 meters tall. It has an upright, branching stem, which sometimes has a woody base. Its leaves are arranged oppositely. Leaf blades grow up to 8 to 10 centimeters long, are oval in shape with sharply toothed edges, and have a rough or wrinkled texture on their upper surfaces. The inflorescence is a very narrow spike up to 40 to 45 centimeters long, covered in pointed bracts. Individual flower corollas bloom from between these bracts. Flowers range in color from deep purple-blue to lavender with pale centers, and white-flowered individuals have been recorded. Each flower lasts only one day before wilting.
The species was named for Cayenne, the capital of French Guiana. In some regions, this plant is simply naturalized. It can be a casual weed, a "garden thug", a crop pest, or an invasive species that impacts local ecosystems. It is well adapted to disturbed, cultivated, and wasted land, growing in pastures, cropland, and along roadsides. In grazed fields, it spreads rapidly because livestock find it distasteful and avoid it, selectively grazing other vegetation instead. It can form thick dense stands in rainy regions, and also persists easily in dry areas.
In Florida, this Stachytarpheta is often confused with the closely related native species S. jamaicensis. Its attractive flower clusters attract butterflies, and 98 different butterfly species have been observed visiting it within its native range. It is mistakenly sold as the native ornamental, planted, and becomes established, after which it can become a noxious weed. Hybrids between the two species occur when this species is introduced. Intentional ornamental planting is a common way this plant spreads. It is also introduced when its seeds are transported via garden waste, rainwater, fodder, contaminated seed shipments, and on vehicles. Control methods include cutting the plants down or pulling them up, with care taken to remove the large roots. Herbicides such as glyphosate are also used for control.
This plant has uses in traditional medicine. Several Latin American groups use plant extracts to treat malaria symptoms. Boiled juice or tea made from the leaves or whole plant is consumed to relieve fever and other symptoms. It is also used for dysentery, pain, and liver disorders. Leaf tea is taken to help control diabetes in Peru and nearby areas. Laboratory tests have confirmed that the plant has anti-inflammatory properties.
