Clearweed is an erect native annual plant of moist and shady places, usually under a foot high, but up to two feet, that has a smooth stem that appears somewhat translucent. There are no stinging hairs on this member of the nettle family.
The egg shaped leaves are opposite, long stalked (stalks often as long as the leaf blade), shiny, and coarsely toothed and have a distinctive set of 3 main parallel veins. Like the stem, they appear translucent.
The inflorescence consists of small branching clusters from the leaf axils near the top of the plant in a manner that resembles the Wood Nettle. These may be densely flowered or more open.
The flowers are greenish-white to greenish-yellow and very small - about 1 mm wide. Male and Female flowers are separate. Male flowers have 4 stamens and tepals (a functionally combined petal and sepal) and in the center a false pistil (a pistillode). Female flowers have 3 lanceolate tepals and one pistil. There are 3 false stamens (staminodes) opposite the tepals. In some female flowers one tepal enlarges and become hood-like. Flowers are wind pollinated.
Seed is a small ovate light colored achene, 1.3 to 1.7 mm long, smooth surface or with some minor striations; and distributed by the wind. They are free of the perianth of the flower but sometimes covered by that enlarged tepal.
Habitat: Clearweed is a woodland plant liking moist to wet rich soils, light shade to partial sun. It propagates by re-seeding.
Names: The species name pumila means "dwarf" referring to the short stature of the plant. The genus Pilea has over 600 species and the name is derived from Latin pileus, or "felt cap", resembling an old Roman hat, and is descriptive of the the enlarged tepal covering the achene (the dry fruit). The author names for the plant classification are: First to classify was '(L.)' which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was amended by ‘A.Gray’, which refers to Asa Gray (1810-1888), American botanist, Professor of Natural History at Harvard and instrumental in unifying plant knowledge of North America and author of Gray’s Manual - Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive.
Comparisons: The other members of the nettle family in the Garden are the Stinging Nettle, Urtica dioica, and the Wood Nettle, Laportea canadensis. The other species of Pilea found in the state, P. fontana, the Lesser Clearweed, has dark seeds with raised bosses, and the leaves do not look translucent and is usually found in bogs.
Above: Clearweed is an annual growing from wind dispersed seeds. As shown above along the path in the Woodland Garden you will usually find them growing in small groups.
Below: 1st photo - Note the smooth translucency of the stem and leaf stalk and the small size of the visible flower heads. 2nd photo - The distinctive leaf with large teeth and a set of 3 main parallel veins.
Below: Comparison drawings of Clearweed and Wood Nettle. Both drawings ©Flora of North America.
Below: Clearweed beginning to bud-out.
Notes: Clearweed was not listed on Eloise Butler's list of indigenous plants of the Garden. By the time of Martha Crone's 1951 census it was listed. Clearweed is native to Minnesota in a number of scattered counties in the southern 2/3rds of the State, especially the counties bordering our major rivers and those bordering Wisconsin where the plant is represented state wide. In North America it is found in the eastern Canadian Provinces from Ontario eastward and in the lower 48, it is a plant of the eastern 2/3rds of the country from the Dakotas southward to Texas and then east to the coast.
There are two species of Pilea found in Minnesota - P. pumila, Canadian Clearweed; and P. fontana, Lesser-Clearweed.
The usual references on plant lore and medicinal properties of plants do not mention this plant. There is one species of Pilea known to be used in Chinese medicine.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"