Virginia Three-seed Mercury: Are They a Weed or a Wildflower?

It all depends on the name and—just maybe—your opinion. When talking about three-seed Mercury, it is important to know its scientific name, as the same common name is applied to two similar plants.

• Acalypha rhomboidea, known by the common names rhomboid Mercury, common three-seed Mercury, copper leaf, rhomboid copperleaf, and Virginia three-seed Mercury, is generally considered a weed, but some consider it an annual native wildflower.
• Acalypha virginica, known by the common names Virginia copperleaf, Virginia Mercury, and (also!) Virginia three-seed Mercury is also considered a summer, annual weed.

For the remainder of this article, Acalypha rhomboidea will be referred to as rhomboid Mercury and Acalypha virginica as Virginia copperleaf. Until recently, rhomboid Mercury was considered a variety of Virginia copperleaf, but it is now regarded as a distinct species. Both are native to eastern and central North America and are members of the spurge family (Euphorbiaceae). Unlike many other members of the spurge family, their stems do not exude a milk-like sap. Both plants are considered mildly poisonous to humans and, if ingested, may cause vomiting and diarrhea.

While both plants may be found in natural habitats such as open woods, forest edges, and grasslands, they are often most abundant in areas of human disturbance, such as vacant lots, roadsides, and other areas of disturbed soil where there is little competing vegetation. These plants require direct sun and exposed soil to germinate and typically do not emerge until the soil temperature warms in late spring or early summer. By that time, many other plants will have already become established, which is one reason that they tend to do best in areas of disturbed soil where there is less competition.

Similar in size and appearance, they grow 1 to 2 feet tall with leaves positioned alternately on the stems in an ascending spiral, growing closer together at the top of the stem. Their 1- to 3-inch serrated leaves are wider at the base and taper to a point at the tip. The leaves turn a copper color in the fall. From mid-summer until frost, tiny inconspicuous green male and female flowers are found on the same plant. The flowers grow from bracts, which are modified leaves, usually smaller in size than the foliage leaves. The bracts form in the axis where the leaf joins the plant stem. Within each bract, there is a short spike of male staminate flowers as well as 1 to 3 female pistillate, flowers which, after being pollinated, produce a three-lobed spheroid fruit. Each of the three lobes contains just one seed. Birds eat the fruit and disperse the seeds. Virginia copperleaf differs from rhomboid Mercury by having hairier stems, narrower leaves, and slightly longer spikes that extend beyond the lobes of the bracts, but the easiest way to differentiate them is by the number of lobes on their bracts. Virginia copperleaf has 10 to 15 lobes on its bracts, while rhomboid Mercury has 5 to 9.

Generally, both species are viewed as nondescript weeds. They are not considered invasive and may be managed easily by hand weeding as they have easy-to-remove shallow tap roots. It is recommended that the gardener wear gloves while weeding as the sap may cause contact dermatitis. In some instances, these two plants may be used in a garden, especially as a ground cover, as they slightly resemble pachysandra