Pilea pumila is an annual herb 10-50 cm tall; translucent; smooth, pale green to pinkish in strong light; roots associated with VA mycorrhizas (Brundrett and Kendrick 1988); Stipules
Leaves opposite, shiny, stalk about half as long as blade, ca over 2.5 cm long (Hilty 2006; Radford et al. 1968); blade 3-10 cm long, egg-shaped, coarsely blunt-toothed, tip long-pointed by terminal tooth, base blunt, major veins 3, conspicuous, often pinkish, palmate, secondary veins ladder-like between primaries; leaf texture membranous, green above, pale to whitish below.
Flowers greenish-white to greenish-yellow, about 0.3 cm long, male and female flowers separate (monoecious), no petals, male flowers with 4 sepals and 4 stamens, female flowers with 3 sepals, 1 pistil, (Hiltly 2006); self-fertile, but also adapted for wind pollination (Cid-Benevento 1986); Inflorescence branched, to about 2.5 cm long, one-sided, in leaf axils; blooms July-Oct.
Fruit dry, oval flattened achenes, pale green, often with blackish ridges, about 0.2 cm long, 0.1 cm wide; fruits Sept.-Oct. (Radford et al. 1968; Hough 1983), wind dispersed (Hilty 2006), viable in soil for less than 2 years.
Wetland status: FACW.
Frequency in NYC: Infrequent.
Habitat: Wet partial to full shade. Not tolerant of full sun or open areas with high temperatures that increase transpiration rates (Cid-Benevento 1986). Increases in forest gaps (Moore and Vankat 1986).
Notes: Leaves fed upon by larvae of: Nymphalis milberti (Milbert’s tortoiseshell), Polygonia comma, (comma), P. interrogationis (question mark) and Vanessa atalanta (red admiral), all of family Nymphalidae (brush-footed butterflies), (Hilty 2006; Pyle1981).