Description: This native annual plant is
½–2' tall, branching occasionally in the upper half. The stems are
smooth, round, hairless, and translucent. They are light green, greyish green,
or reddish green in appearance;
some of the large stems may be slightly ribbed. The
opposite leaves are 1-5' long and half as much across. They are ovate,
hairless, and coarsely serrated. Each leaf has a thin membranous texture with a
prominent central vein and two conspicuous side veins. The upper surface is
green or dark green, while the lower surface is light green or nearly white.
The petioles of the leaves are quite long, frequently 1" in length or more.
From the axil of each upper leaf, there develops a narrow raceme of flowers up
to 1" long. This raceme is usually shorter than the petiole, slightly curved,
and more or less horizontal. Each plant has separate male and/or female flowers
that are less than 1/8" long, and either greenish white or greenish yellow. The
male flowers have no petals, 4 sepals, and 4 stamens, while the female flowers
have no petals, 3 sepals, and 1 pistil. Toward the inner surface of the sepals
are small scales. The blooming period occurs from mid-summer to early fall, and
lasts about 1-2 months. There is no floral scent. The tiny achenes are green,
sometimes with black stripes. They can be blown about by the wind, and in this
manner are dispersed.
Cultivation:
The preference is light shade and moist to wet conditions. This plant usually
grows in rich woodland soil. The foliage is little bothered by disease and is
quite attractive. Standing water is tolerated if it is
temporary.
Range & Habitat:
Clearweed is a common woodland plant that occurs in almost all counties of
Illinois (see
Distribution
Map). Habitats include poorly drained areas of upland forests, floodplain
forests, crevices in rocky canyons, and shady or partially shaded wetland
areas, including seeps, borders of small streams,
and
alongside pools of water. The moist wooded areas where this plant occurs are
typically dominated by such deciduous trees as Silver Maple, Sugar Maple,
Sycamore, River Birch, Green Ash, etc. Clearweed often forms large colonies by
reseeding itself.
Faunal
Associations: The flowers are wind-pollinated, therefore they don't
attract many insects. The caterpillars of the following butterflies feed on the
foliage: Nymphalis milberti (Milbert's Tortoiseshell), Polygonia
comma (Comma), Polygonia interrogationis (Question Mark), and
Vanessa atalanta (Red Admiral). These caterpillars feed on other members
of the Nettle family as well.
Photographic
Location: The plants were growing in a shady area along a small
stream at Meadowbrook Park, Urbana, Illinois.
Comments: The most unusual characteristic of this
plant is the translucency of the foliage – this has been useful in biology
classes to show the uptake of liquids from the roots into the stems and leaves.
A less common species of Clearweed, Pilea fontana, has stems that are
less translucent and its achenes are black, rather than green. Clearweed
resembles other members of the Nettle family as well, but it lacks the stinging
hairs that can be found on Urtica dioica (Stinging Nettle) and
Laportea canadensis (Wood Nettle). While Boehmeria cylindrica
(False Nettle) lacks stinging hairs, its stems aren't translucent and its
racemes of flowers are more erect and longer than Clearweed's
racemes.