Description: This native plant is a summer annual
about 1–2½' tall, branching occasionally. The stems are round or
somewhat angular and they have spreading white hairs. The alternate leaves are
up to 4" long and
2" across. They are rather thin-textured
and have raised veins on their undersides. The leaves are cordate or broadly
ovate and serrated along the margins. The long slender petioles often have
spreading hairs like the stems. Hornbeam Mercury is monoecious with separate
male and female flowers on the same plant. The male or staminate flowers
develop from the axils of the leaves in non-terminal spikes about
½–2" long. These staminate spikes are densely crowded with small
flowers and cylindrical in appearance. Each male flower is about 1/8" across,
consisting of 4 sepals that are green or translucent white, several stamens and
anthers that are white, and no petals. The spikes of female or pistillate
flowers terminate the upper stems; they are usually located above the male
flowers. The pistillate spikes are also densely crowded with small flowers, but
their appearance is less smooth and cylindrical than the staminate spikes
because of the long styles and floral bracts. Each female flower is about
¼" across, consisting of several long branching styles that are white, a
3-valved green capsule that is quite spiny in appearance, a surrounding floral
bract that is green with several narrow lobes, and no petals. The blooming
period occurs from mid-summer to early fall and lasts about 1-2 months. The
flowers are pollinated by wind. Each valve of the capsule in a female flower
contains a single seed. The seeds are ovoid in shape, broader and rounder at
one end than the other, and pitted or wrinkled across the surface. The root
system consists of a taproot. This plant spreads by reseeding itself, and
occasionally forms colonies.
Cultivation: This plant is typically found in full
or partial sun, moist to mesic conditions, and a fertile loamy soil. It also
occurs in clay-loam and stony soil. At locations that are too hot and dry, the
foliage often wilts.
Range &
Habitat: Hornbeam Mercury occurs occasionally in the southern half
of Illinois (see
Distribution
Map). Habitats include thickets, riverbanks, bluffs, cropland, fallow
fields, gardens, areas along buildings, and roadsides. This native species
prefers disturbed areas and is a minor pest of cropland in the southern half of
the state.
Faunal Associations: The
flowers don't attract many insects because they're wind-pollinated. The seeds
are occasionally eaten by upland gamebirds and seed-eating songbirds, including
the Mourning Dove and Bobwhite. Deer browse on the foliage of the herbaceous
Acalypha spp. that occur in the state, and possibly other mammalian
herbivores do this as well. It is possible that the foliage is mildly toxic to
cattle, possibly because of excess nitrate accumulation. Unlike many other
members of the Spurge family, the native Acalypha spp. lack a toxic
white latex in their foliage.
Photographic
Location: A few plants were growing along the foundation of the
webmaster's apartment complex in Urbana, Illinois.
Comments: Hornbeam Mercury is a nondescript plant
that is easily overlooked. Its leaves are supposed to resemble the leaves of
the Hornbeam tree, hence the common name. Another common name is Rough-Podded
Copperleaf, which refers to the spiny-looking seed capsules and the tendency of
the foliage to turn reddish brown during the fall. Hornbeam Mercury differs
from other native Acalypha spp. by its monoecious flowers (separate
spikes of male and female flowers) and its broad serrated leaves that are
heart-shaped at the base. The leaves remind me of the foliage of woodland
plants in the Nettle family, but Hornbeam Mercury occurs in sunnier habitats
and the female flowers are surrounded by the lobed bracts that are typical of
native Acalypha spp. in Illinois.