Clearweed (Pilea sp.)

Clearweed is distinctive and easy to identify.  The leaf shape and growth habit resembles stinging nettles.  The leaves are fairly broad, are simple, and have fairly large and regular teeth, and are arranged oppositely along the stem.  Each leaf has three prominent veins.

Unlike other plants of the nettle family, clearweed lacks stinging hairs: the stem and leaves are hairless.  Clearweed also has conspicuously translucent stems and leaves.  The foliage often looks shiny.

These plants are small relative to other members of the nettle family, typically reaching a max height of 2 feet, usually much less.  Early in the season, they will be only a few inches high.

Clearweed is happiest in light shade and wet conditions.  It likes poorly-drained areas, and can tolerate standing water temporarily, but cannot live in permanently flooded wetlands.

As an annual, clearweed dies down each year, but it can form persistent colonies through self-seeding.  The plant doesn't usually get very large; maximum height is usually around 2 feet, but it is common for plants to only reach about 6-12 inches in height.

The root system is weak and shallow, forming a small clump at the base of the stem.  The shallow roots are connected to this plant's preference for wet areas: the plant will wilt if the soil becomes thoroughly dry for too long.  Because of its weak roots, this plant is easily disturbed if weeding other plants growing in it.  Be gentle and take care to not disturb this plant if you wish to spare it while weeding.

The caterpillars of a number of different butterflies, ones that specialize in plants of the nettle family, feed on the plant's foliage, including the rather attractive Milbert's Tortoiseshell (Nymphalis milberti), Polygonia comma (Comma), the Question Mark Butterfly (Polygonia interrogationis) , and the Red Admiral (Vanessa atalanta).  For such an inconspicuous plant, these butterflies are quite visually striking.

The larvae of a rather interesting moth called the Beautiful Cosmopterix Moth (Cosmopterix pulcherimella) also eats the leaves. There is also an aphid, Pseudasiphonaphis corni, which feeds on the sap from the stem, and a leafhopper, Empoasca recurvata, that feeds on this plant among many others.

The neat, orderly appearance and interesting leaf shape and structure make this plant a useful and visually-striking landscape plant.  It also is useful as it thrives in wet, shady conditions that fewer plants like.  The flowers are wind-pollinated and are as such inconspicuous and easily overlooked; it is the foliage that makes this plant interesting to look at.

Because it is an annual, clearweed can only be grown persistently where the conditions are right.  If you want to grow it, scatter seeds or transplant a few plants to a wet, partially-shaded area of your garden, and you can let it form a colony, functioning a little like a groundcover.

Because it is shallow-rooted, it does not hold soil well.  It is thus best grown in flat, low-lying depressions surrounded by higher ground, or it can be mixed with deeper-rooted plants that hold the soil more effectively.

• Clearweed | Illinois Wildflowers - This site focuses on Illinois, but has useful information about this plant overall as well.
• Pilea pumila (Clearweed) | Wikipedia - A small and ever-evolving article on this plant.
• Pilea pumila | USDA Plants Profile - The official USDA page for this plant, including range maps.