Pilea pumila (Dwarf Clearweed)

Plant Info
Also known as: Canadian Clearweed
Genus:Pilea
Family:Urticaceae (Nettle)
Life cycle:annual
Origin:native
Habitat:part shade, shade; moist shaded woods, wetlands, wooded shores
Bloom season:July - September
Plant height:4 to 20 inches
Wetland Indicator Status:GP: FAC MW: FACW NCNE: FACW
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle Cluster type: whorled

[photo of flowers] 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: Leaf attachment: opposite Leaf type: simple

[photo of leaves] 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.

Fruit: Fruit type: seed without plume

[photo of fruit] Fruit is a flattened, teardrop shaped seed, up to 1/16 inch long and about half as wide as long.

[photo of seed] Surfaces are patterned with random dark purple to black spots against light green, but rather variable in the amount of green to black.

Notes:

Pilea pumila is one of two native clearweeds in Minnesota, the other is Black-fruited Clearweed (Pilea fontana). They are nearly impossible to distinguish but for the size and color of their fruit (achenes), and only when fruit is present. As described, P. pumila's fruit is smaller and proportionately narrower, with scattered dark pigment spots against light green. P. fontana's achene is larger, proportionately broader, solidly dark pigmented but for a narrow green edging. Typically the difference is distinguishable with the naked eye with the larger, darker fruit of P. fontana standing out 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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More photos

Photos courtesy Peter M. Dziuk taken in a private wooded garden in Anoka County and at Westwood Nature Center in Hennepin County. Seed photos courtesy Rick Haug.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Leo - Ramsey county, Mounds View
on: 2013-09-06 19:33:13

This is the first year I have noticed this clearweed in our garden and flower beds in the back yard.

Posted by: Bill - Minnetonka
on: 2014-09-01 16:01:37

We live in the Minnetonka area. This is the first year I've become aware of clearweed. I first removed a lot of buckthorn for several years, then garlic mustard moved in and I tried to control that. Now clear weed has covered the understory of the back woods previously covered by the two previous weeds. Am I winning or losing?

Posted by: K. Chayka
on: 2014-09-01 20:02:57

Bill, chances are clearweed was in your woods before the invasives arrived. It is native, after all, and moist woods is suitable habitat.

Posted by: Linda - Lebanon Hills Regional Park, Eagan MN
on: 2015-08-29 02:23:41

Thanks for the photos. I'd been wondering what this bright green plant was that soon carpeted the edges of trails that were widened or where we had removed dense garlic mustard stands.

Posted by: Craig B - Ham Lake
on: 2017-07-22 15:18:15

We are getting tons of this the last few years. We have a very shady lot and it is running rampant in our flower beds...even in our lawn and areas where we're trying to cultivate moss. How can we get rid of it?

Posted by: jerry k - on rice creek, Fridley, Anoka County Minnesota
on: 2017-09-03 19:37:47

I too found that this plant seems to profit from the eradication of garlic mustard. It must be that the allelopathic effects from the garlic mustard at least benefit this one native species. It wasn't very common before the garlic mustard invasion, but after eliminating the garlic mustard, it now totally blankets the forest floor in my back yard. Glad to discover it's native at least! Hopefully the native microbiota in the soil will recover and other native species will return.

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