Trans. Linn. Soc. London 12: 156. 1818.
Shrubs, spreading, open, rounded, 10–20 (–30) dm; rhizomatous, suckering freely. Stems 1–30+, widely arcuate, sparingly branched; bark (periderm) not forming, epidermis green, striate, glabrous; short-shoots absent; unarmed; bud-scales imbricate. Leaves winter-deciduous, cauline, alternate; stipules caducous, linear-subulate, thin, margins entire ± strigose-ciliate; petiole present; blade ovate to lanceovate, 2–8.5 cm, membranous, margins flat, coarsely doubly serrate, abaxial surface sparsely sericeous-strigose along veins. Inflorescences terminal on vernal, leaf-bearing lateral branches, flowers solitary, sparsely strigose or glabrous; bracts absent; bracteoles absent or present, leaflike. Pedicels present. Flowers 20–50 mm diam.; epicalyx bractlets 0; hypanthium saucer-shaped, 3–4 mm diam., glabrous; sepals (4 or) 5 (or 6), spreading to reflexed, oblong-ovate to ± orbiculate; petals (4 or) 5 (or 6), to 34 in multi-petaled cultivars, spreading, strong yellow to slightly orangish or yellow-cream (some petals white in multi-petaled cultivars), oblong-ovate to orbiculate, base short-clawed, apex rounded to emarginate; stamens 80–130 (0 or few in multi-petaled cultivars), shorter than petals; torus absent; carpels (4–) 5 (–8), globose, glabrous, styles lateral, linear, ± exceeding filaments; ovules 2. Fruits aggregated nutlets, (1–) 5 in 1 whorl, tan, obliquely obovoid-globose, 4.5–5 mm, with distinct adaxial ridge, glabrous except for coarse basal hypanthial hairs; hypanthium persistent; sepals persistent (withering), reflexed; exocarp thin, wrinkled, mesocarp thin, dry, endocarp ± cartilaginous. x = 9.
Introduced; e Asia (China), e Asia (Japan), also in Europe
Kerria is a distinctive mesophytic shrub, native to montane forests and valleys at 200–3000 m in China and Japan, now widely cultivated. Morphologically, it stands closest to Neviusia.
"thin" is not a number.