Pilea microphylla
Pilea fontana
artillery plant, artillery weed, pistol plant, rockweed
clearweed, lesser clearweed
10-40-branched, erect.
simple or slightly branched, erect.
blades spatulate to obovate, paired blades unequal, the larger 3-10 × 1.5-5.5 mm, the smaller 1.5-4 × 0.7-2 mm, margins entire.
blades elliptic to ovate, paired blades equal, 1-10 × 0.6-4.5 cm, margins dentate.
crowded.
crowded or lax.
ca. 0.5 mm across.
ca. 1 mm across.
uniformly light brown, slightly compressed, ovoid-cylindric, ca. 0.5(-1.1) × 0.3 mm, smooth.
uniformly black except for very narrow, pale, often inconspicuous, marginal band, compressed, teardrop-shaped, 1.3-1.7 × 1-1.5 mm, conspicuously pebbled or warty with raised bosses.
Pilea microphylla
Pilea fontana
Pilea microphylla has been collected once in Tennessee and once in Michigan, but it is unlikely that the species persists so far north. It is widely grown as a houseplant in the north and a border plant in the south. It is a greenhouse weed in various parts of the flora.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Pilea fontana and P. pumila are separated primarily by differences in their mature achenes. In addition, leaves of P. fontana are often more opaque and less shiny than those of P. pumila. A few collections of P. pumila from Bourbon, Owen, and Robertson counties, Kentucky, and Macon County, Tennessee, have the black achenes of P. fontana, but without the bosses, and show striations on the younger achenes as in P. pumila. I have seen only two mixed collections (Chisago County, Minnesota, and Richland-Ransom county line, South Dakota), which probably indicates that these two very similar species seldom occur together, even though their ranges overlap completely.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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