Pilea
Coll. Bot., plate 4 and text on facing page. 1821, name conserved.
Herbs, shrubs, or subshrubs, annual or perennial, glabrous. Stems simple or branched, erect, ascending, or repent. Leaves opposite; stipules present. Leaf blades paired, equal or unequal, ovate, margins dentate or entire; cystoliths linear, ± conspicuous. Inflorescences axillary, compact to lax cymes. Flowers unisexual, staminate and pistillate flowers in same cyme; bracts deltate to linear. Staminate flowers: tepals 4; stamens 4; pistillode conic. Pistillate flowers: tepals 3, equal or sometimes 1 tepal enlarged and hoodlike; staminodes 3, opposite tepals, under tension and ejecting mature achene; style and tufted stigma deciduous. Achenes sessile, laterally compressed, ovoid to teardrop-shaped, free from perianth at maturity, partly covered by hoodlike tepal. x = 12, 13.
Distribution
Mostly tropical and subtropical regions worldwide except Australia and New Zealand.
Discussion
Species ca. 400 (5 in the flora).
Pilea should be further revised.
Selected References
Lower Taxa
Key
| 1 | Leaf margins dentate; paired blades equal. | > 2 |
| 1 | Leaf margins entire; paired blades unequal. | > 3 |
| 2 | Achenes uniformly black except for very narrow, pale, marginal band, surface conspicuously pebbled with raised bosses. | Pilea fontana |
| 2 | Achenes uniformly light colored or streaked with purple, surface smooth or purple striations sometimes slightly raised. | Pilea pumila |
| 3 | Stems repent or prostrate. | > 3 |
| 3 | Stems erect or diffusely ascending. | > 4 |
| 4 | Herbs; leaf blades spatulate to obovate. | Pilea microphylla |
| 4 | Shrubs or subshrubs; leaf blades of 2 types, obovate and orbiculate to orbiculate-cordate. | Pilea trianthemoides |