Virginia Threeseed Mercury vs Slender Threeseed Mercury
These two species are easily confused as they are visually similar, overlap in range, can occur together in the same habitats, and have sometimes-overlapping characteristics of leaf shape. They can usually be easily distinguished by examining lobe length of the bracts, and/or the pubescence on the stems and bracts. There are also differences in leaf shape and petiole length. A. gracilens has a more southerly distribution, but has been expanding its range northward; it also has a greater preference for sandy and/or rocky soils and flat terrain, whereas A. virginica prefers slightly richer soils and is more likely in sloped or hilly terrain.
Virginia Threeseed Mercury (Acalypha virginica) | Slender Threeseed Mercury (Acalypha gracilens) |
An inconspicuous weedy annual native to eastern to central North America. Its name is midsleading: although it occurs in Virginia, it is more common farther north and west. | An annual native mostly to the southeastern US. |
 Bract lobes are deeper-cut, usually 1/4–1/2 the length of the bract. Central lobe is not appreciably larger than others, and contains a single vein. Underside of bract is densely pubescent. Photo © , CC BY-SA 4.0. |  Bracts lobes have shallower cuts, usually 1/10–1/4th the length of the bract. Central lobe is often much larger than others, encompassing multiple veins. Pubescence on underside of bract is much sparser. Photo © Abby Darrah, CC BY 4.0. |
 Petioles (stem connecting leaf to the main stem) average slightly longer, usually 1/3rd to 1/4th length of leaf blade. Photo © Melissa McMasters, CC BY 4.0. |  Petioles average slightly shorter, usually 1/4 of leaf blade or shorter. Photo © Christopher Warneke, Public Domain. |
 Stem covered (usually densely) in stiff hairs, which project outward perpendicular to the stem. Photo © Melissa McMasters, CC BY 4.0. |  Stems average less pubescent, hairs are shorter, softer, and tend to be pressed against the stem. Photo © Evan M. Raskin, CC BY 4.0. |
 Leaves average slightly broader (0.5–3mm wide) and broader relative to their length. Serrations are slightly more pronounced and always visible. Photo © , CC BY-SA 4.0. |  Leaves average slightly narrower (0.4–2mm wide) and broader relative to their length. Serrations are less pronounced and may even be barely visible on some plants. Photo © Jay Horn, CC BY 4.0. |
 Although many plants have similar leaf tips (see above photos), some have strongly pointed tips, which can exclude A. gracilens. Photo © Samantha Heller, CC BY 4.0. |  Although many plants have similar leaf tips, some plants have conspicuously blunt leaf tips, which can exclude A. virginica. Photo © Amber M. King, CC BY 4.0. |
References & External Resources
These short lists show only links helpful for ID. For a complete list of references and resources also covering other aspects of ecology, visit the links section of the full article on each plant, which is the first entry here.
