64. Pilea pumila (Linnaeus) A. Gray, Manual. 437. 1848.
透茎冷水花 tou jing leng shui hua
Herbs annual, subglabrous, monoecious. Stems erect, simple or branched, 5-50 cm tall, succulent. Stipules soon deciduous, ovate-oblong, 2-3 mm, membranous; petiole subequal in length, 0.4-4.5 cm, sparsely puberulent adaxially; leaf blade spreading, rhombic-ovate or broadly ovate, subequal in size, 1-9 × 0.6-5 cm, membranous, 3-veined, lateral veins several, distal ones anastomosing, others inconspicuous, both surfaces sparsely pilose, cystoliths linear, base often broadly cuneate, or proximal ones obtuse, margin dentate-serrate, apex shortly acuminate, caudate, or acute; proximal leaf pair often entire. Inflorescences often androgynous, solitary, from almost every node, male a scorpioid cyme, shorter, in the lower nodes, subsessile, many flowered; female inflorescence larger, in upper nodes, in fruit enlarged, but often shorter than petioles. Male flower pedicellate or sessile, in bud obovoid, ca. 1.8 mm; perianth lobes 2(-4), cymbiform, connate at base, subapically corniculate; stamens 2(-4); rudimentary ovary inconspicuous. Female perianth lobes free, subequal or lateral ones slightly larger, all oblong-cymbiform, as long as achene in fruit. Achene often with brownish dots, triangular-ovoid, 1.2-1.8 mm, compressed, smooth. Fl. Jun-Aug, fr. Aug-Nov.
Moist places in forests, ravines, by rice fields, walls by villages; 300-2200(-2900) m. Anhui, Chongqing, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Ningxia, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Japan, Korea, Mongolia, Russia (Siberia); North America].
Populations of this species from E Asia were described as Pilea mongolica. The authors have examined material of this species, including plants from Asia and North America, and found the specimens were consistently characterized by the scorpioid cyme, 2(–4)-merous male flowers, and triangular-ovoid achene. There is no reason to separate populations from E Asia as a separate species. However, three varieties are recognized here.
The plants are used medicinally as a diuretic.