August 2010: Phyllanthus Urinaria L., The Chamber Bitter Or Gripe Weed

Botany

August, 2010: Phyllanthus urinaria L., the chamber bitter or gripe weed

A warm-season annual weed that has become an obnoxious pest in gardens, home landscapes and other cultivated areas..

Phyllanthus urinaria, showing underside of side branches, with warty fruits and flowers.
Photograph courtesy of Matthew Merritt, Atlas of Florida Vascular Plants

 Family: Euphorbiaceae, the Spurge Family

Distinguishing Characteristics: This is an annual plant with the main stem erect, unbranched or sparsely branched and seldom more than a foot tall. The side branches with their two rows of alternate leaves resemble a compound leaf. The leaves themselves are finely hairy, nearly sessile (stalkless), oblong to narrowly obovate, blunt at the apex, and ½ - ¾ inch long. The unisexual flowers are whitish, tiny and inconspicuous, and they are borne singly or in small clusters in the axils of the leaves. The female flowers develop rapidly after pollination to produce sessile, roundish, slightly flattened, rough-textured capsules. These capsules are about 1/8 inch in diameter when ripe, and are held beneath the leaves.

Phyllanthus urinaria, mature plants.
Photograph courtesy of John Kunzer, Atlas of Florida Vascular Plants

Distribution: It is believed that the plant originated in tropical Asia, but it has become a pantropical weed. In the United States it is established throughout the Southeast, from Virginia to Texas, as well as in Puerto Rico. It has also been reported from a single county in Illinois.

Occurrence in Florida: The plant is common throughout the state, primarily in cultivated areas such as lawns, gardens, home landscapes and nurseries. It thrives in sun or shade. So far, it has not become invasive in natural areas.

Similar Species in Florida: The Mascarene Island leafflower, Phyllanthus tenellus, is also a common weed, and similar to P. urinaria but somewhat less prolific. It is more open and delicate in appearance, with more widely spaced leaves, and its fruits are on slender stalks, rather than being sessile. The native P. caroliniensis, a plant of wet hammocks and marshes, has fruits and leaves on the main stem, rather than only on the side branches as in P. urinaria, and its fruits are smooth rather than warty.

Phyllanthus urinaria, showing fruits and leaflike side branches.
Photograph courtesy of Dennis Girard, Atlas of Florida Vascular Plants

Means of Dispersal: This is an annual plant, and it does not sucker or root at the nodes, so it depends entirely on its seeds for dispersal. These are tiny, less than 1/16 inch across, and are borne profusely throughout the season. They are easily dispersed on gardening utensils, on shoes, by rainwater etc.

Comments: Phyllanthus urinaria is a warm-season annual, and seedlings do not appear here in northern Florida until May. The plants produce seeds throughout the season and begin to senesce in September, and then seedlings also become less profuse. Glyphosate and other herbicides are effective for control, especially at the seedling stage, but manual removal is often necessary in garden situations. This can be frustrating, because the roots are tenacious and firmly anchored in the soil, and it is often difficult to remove the plant intact. Chamber bitter is an important medicinal herb in tropical Asia, where it is used to treat kidney stones, gallstones, liver diseases and viral infections. Modern clinical studies have found it to be promising in the treatment of various tumors. Even though it is one of the very worst warm-season weeds in northern Florida gardens, it is not regulated by the state or federal government, and it is not on the FLEPPC list of invasive species. Only Alabama considers it to be a noxious weed.

Phyllanthus tenellus, showing stalked fruits.
Photograph courtesy of John Kunzer, Atlas of Florida Vascular Plants

Further Information: http://www.tropilab.com/shatterst.html (Accessed: 29 August, 2010)

Dr. Richard Weaver, Botanist
Florida Department of Agriculture and Consumer Services
Division of Plant Industry
1911 Southwest 34 Street
Gainesville, Florida 32614