The Original Mystery Plant
Dr. John Nelson

Photo by Gary Ward

This little plant looks something like a holiday poinsettia, if you use your imagination, and sure enough, it is related to poinsettia. They both belong in the same genus, and are members of the very large and diverse, mostly tropical plant group, euphorbiaceae or "spurge" family. While the holiday poinsettia is a perennial species, this little weed is a tender annual.

It produces plenty of egg-shaped leaves alternating up and down the smooth stem. Vigorous, robust individuals sometimes grow to be two feet tall or more. The leaves and stems, if broken or cut, ooze or drip white sap, sometimes copiously. (We call this sap "latex.") The upper leaves are much different in shape from those below, usually with a narrowed waist and thus fiddle- shaped. These bracteal leaves tend to have a conspicuous blotch of red--or pink--at the base, clustered just below the flowers. The flowers themselves are extremely tiny and inconspicuous, held inside greenish-yellow cup-shaped structures easily visible above the bracts. You may recall from poinsettia lore that the beautiful red petals are not at all parts of the flower but are themselves bracteal leaves.

Photo by Linda Lee

The mystery plant is probably native to the central and southeastern U.S., but it's hard to tell exactly. It is able to get around rather easily from seed, typically growing in disturbed places. For this reason it is something of a weed often springing up spontaneously at the edge of the yard or garden, sometimes in abundance. This species has achieved a reputation as a more serious pest in tropical areas including the Pacific islands (especially Hawaii), but here in the South it is generally fairly benign, not too much of a pest. To get rid of it, consider pulling it up rather than using herbicides. It pulls up easily.

It shows up regularly in summer, giving off some unexpected winter cheer.

Answer to last week's mystery plant

Smooth ground-cherry, Physalis angulata

Dr. John Nelson is the curator of the USC Herbarium.

To learn more about the Herbarium, call him at

777-8196. His department also offers free plant identification.

www.herbarium.org