Manual, 437. 1848
Herbs, 0.7-7 dm. Stems simple, erect. Leaf blades elliptic to broadly elliptic or ovate, paired blades equal, 2-13 × 1-9 cm, margins dentate. Inflorescences crowded to lax. Flowers ca. 1 mm across. Achenes uniformly light colored or with streaks of purple, compressed, teardrop-shaped, 1.3-1.7 × 0.6-1.1 mm, smooth or purple striations sometimes raised. 2n = 24, 26.
Phenology: Flowering summer–fall.
Habitat: Moist to wet woods, woodland margins, along streams, shaded waste places
Elevation: 0-2000 m
N.B., Ont., P.E.I., Que., Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis., Asia.
Typical plants have leaf blades with cuneate bases and 3-11 rounded teeth on each margin; plants with rounded leaf bases and 11-17 less rounded or acute teeth on each margin have been called Pilea pumila var. deamii (Lunell) Fernald (M. L. Fernald 1936) [Adicea deamii Lunell, Amer. Midl. Naturalist 3: 10. 1913.]. Typical P. pumila also is found in eastern Asia, where three infraspecific taxa, P. pumila var. pumila, P. pumila var. hamaoi (Makino) C. J. Chen, and P. pumila var. obtusifolia C. J. Chen are recognized. This complex, which also includes P. pauciflora C. J. Chen, has been placed in Pilea series Pumilae C. J. Chen. Although the Asian plants are often vegetatively and florally indistinguishable from the North American plants, minor differences do occur in the achenes, especially in their markings and sculpturing when mature. Detailed studies are needed to clarify exact relationships.
Native Americans used Pilea pumila medicinally to alleviate itching, to cure sinus problems, and to treat excessive hunger (D. E. Moerman 1986)