Pilea fontana (Black-fruited Clearweed)
|Also known as:||Lesser Clearweed, Bog Clearweed|
|Habitat:||part shade; wetlands, moist shaded woods, lakeshores, moist prairies|
|Bloom season:||July - September|
|Plant height:||4 to 20 inches|
|Wetland Indicator Status:||GP: OBL MW: FACW NCNE: FACW|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Separate male and female flowers, both small and indistinct, green to pale yellow and densely packed in horizontally spreading, irregular panicles about 1 inch long arising from leaf axils in the upper half of the plant.
Leaves and stems:
Leaves are opposite, elliptical to egg-shaped, 1 to 5 inches long, the tip pointed, the base rounded to wedge-shaped, on a stalk about half as long as the leaf blade. Leaves are thin and somewhat translucent with three prominent veins from the base. Surfaces are shiny with scattered short hairs on the upper surface. Edges are toothed, sometimes double toothed. Stems are sometimes branched but usually not, very fleshy and translucent, somewhat squarish, very smooth and shiny.
Pilea fontana is one of two native clearweeds in Minnesota, the other is Dwarf Clearweed (Pilea pumila). They are nearly impossible to distinguish but for the size, shape and color of their fruit (achenes). As described, P. fontana's fruit is broader than P. pumila, and evenly dark pigmented across its surface except for the green edging. P. pumila's achene is proportionately narrower, with scattered dark pigment spots against light green, usually denser towards the ends. As its common name - Black-fruited Clearweed - suggests, the difference is discernible with the naked eye while still in the panicle, though some more darkly pigmented P. pumila may be more easily confirmed by collecting some fruit into the palm of your hand for closer inspection.
Some references note differences in the degree of translucency between the two species, but these are not reliable traits to distinguish them in the field. Even when the two are side by side the differences are too subtle for a positive ID. Of note is that Flora of North America states the two are not often encountered together, even though their habitats and distribution ranges overlap considerably. The leaves of the two Pilea species are similar to other members of the Nettle family, most closely to False Nettle (Boehmeria cylindrica), which has more spike-like flower clusters and leaves more finely serrated with more than 3 prominent veins scattered along the midrib, and Wood Nettle (Laportea canadensis), which has stinging hairs and is a considerably larger plant.
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Photos by K. Chayka taken at Orway Prairie, Pope County. Photos courtesy Peter M. Dziuk taken at Long Lake Park, Ramsey County, Westwood Hills Nature Center, Hennepin County, and at Ordway Prairie. Seed photos courtesy Rick Haug.
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