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. 2 n = 24, 26. Flowering summer-fall. Moist to wet woods, woodland margins, along streams, shaded waste places; 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)
Annual, very smooth and pellucid, 1-5 dm; lvs long-petioled, shining, ovate, 3-12 cm, serrate or crenate-serrate, broadly cuneate to rounded at base, usually glabrous, 3-nerved from the base, the nerves narrowly winged; terminal lf-tooth elongate; cymes 5-30 mm from the middle and upper axils; cal-lobes equal or nearly so; achenes pale green, usually with slightly raised purple spots, 1.3-2 mm, 55-70% as wide as long; seed smooth. Moist, rich, shaded soil, often in colonies; Que. to Minn., s. to Fla., La., and Okla. July-Sept. (Adicea p.) Northeastern plants have the lvs sharply cuneate at base, with 11 or fewer rounded teeth on each side. Toward the s. and w. the lf-base tends to be more rounded, and the teeth sharper and more numerous; this poorly defined phase has been called var. deamii (Lunell) Fernald.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.