Herbs, perennial, clump-forming, 5–15(–20) dm, herbage glabrous or sparsely to densely hairy, ?hairs simple, straight to curved, sometimes multicellular or glandular?; rhizomatous, ?rhizomes thick, branching, woody; roots coarse, fibrous?. Stems 1–5, erect, ?stout, simple, sometimes glaucous?. Leaves deciduous, cauline, alternate, 2–3-irregularly ternate to odd-pinnate, equivalent to 2–3 pinnate; petiole present, ?relatively long, base 1/2 sheathing stems?; blade broadly ovate, ?cauline reduced in size and complexity distally?, 15–60 cm, thick to thin, leaflets 9–45, ?long-petiolulate?, broadly ovate to narrowly lanceolate, margins flat, [serrate to] doubly serrate, venation pinnate. Inflorescences terminal, 500–2500-flowered, racemes forming panicles; bracts present; bracteoles present ?hairs simple, glandular?. Pedicels present. Flowers unisexual (plants dioecious, rarely polygamous), 3–4 mm diam.; epicalyx bractlets 0; hypanthium shallowly bowl-shaped, 0.5–1 mm, ?nectary ring inside with simple, glandular hairs?; sepals persistent, 5, spreading, triangular, ?margins entire?; petals 5, white, obovate to elliptic, ?base cuneate?; staminate: stamens (15–)20(–30) in 1 series (between calyx and nectar ring), longer than petals; torus minute; pistillate: nectar ring scarcely developed, stamens rudimentary, carpels 3, free, glabrous, styles terminal; ovules 2–4. Fruits follicles, 3(or 4), ?pedicels recurving, fruits inverted, retrorse?, ovate-elongate, 1.5–5 mm, ?shining?, glabrous, dehiscent along whole adaxial suture; hypanthium persistent; sepals persistent, spreading to appressed; styles persistent, ?forming a beak?. Seeds 2–4, elongate, ?membranous, caudate at both ends, scalariform-reticulate, seed coat loose?. x = 7, 9.
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Herbs perennial, sometimes woody at base, monoecious. Rhizome robust. Stems erect, angled. Leaves exstipulate, 1–3-pinnate, rarely 3-foliolate; leaflets sharply doubly serrate. Inflorescence a large, spikelike, many-flowered panicle; peduncle and pedicels pubescent and sparsely stellate hairy; bracts and bracteoles linear-lanceolate. Flowers sessile or subsessile, unisexual, rarely bisexual. Hypanthium cupular, with ringlike disc on rim. Sepals (4 or)5(or 6), persistent in fruit, triangular, abaxially glabrous or nearly so, margin entire, apex acute. Petals 5, white, obovate, base cuneate, apex obtuse. Male flowers: stamens 15–30, borne on rim of hypanthium; filaments slender, longer than petals; carpels obsolescent. Female flowers: filaments short; anthers sterile; carpels 3 or 4(–8). Follicles glabrous, pendulous in fruit, dehiscent along adaxial suture. Seeds 2.
Dioecious; fls 5-merous; hypanthium saucer-shaped; sep triangular; pet spatulate to obovate; stamens 15 or more, unequal, vestigial in pistillate fls; carpels 3(4–5), distinct, erect, with divergent styles, capitate stigmas, and several ovules, vestigial in staminate fls; follicles oblong, turgid, ventrally dehiscent; tall, shortly rhizomatous perennial herbs with alternate, exstipulate, 2–3-ternately compound lvs and small white fls in numerous racemes aggregated into a large terminal panicle. Much like Astilbe in aspect, but sharply distinct on floral characters. 10+, N. Temp.
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