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Herbs perennial, dioecious. Taproots large, thick, with remote secondary roots. Stems erect, 40-120 cm tall, glabrous, grooved. Basal leaves oblong-lanceolate to lanceolate, base sagittate, 4-13 × 1.5-4 cm, both surfaces glabrous or veins minutely papillate, margin entire, apex acute, basal lobes acute at apex; cauline leaves small; petiole short or nearly absent; ocrea fugacious, white, membranous. Inflorescence terminal, paniculate, dense, much branched. Flowers unisexual. Pedicel slender, articulate below middle. Male flowers: outer tepals erect, small; inner tepals elliptic, ca. 2 mm. Female flowers: outer tepals reflexed in fruit; inner tepals enlarged in fruit; valves orbicular to broadly ovate, 3-4 mm in diam., with small recurved tubercles at base of valves, base truncate to cordate, margin nearly entire, apex obtuse. Achenes brown, shiny, ellipsoid, trigonous, ca. 2 mm. Fl. May-Jun, fr. Jun-Jul. 2n = 14, 15.
The closely related Eurasian sp. R. thyrsiflorus Fingerh., with a denser infl, the primary branches again branched, and with the lf-lobes often a little more divergent, has been reported in n. Mich. and on the s. side of the St. Lawrence R. in Que.
A herb. It keeps growing from year to year. The taproots are large. It grows 40-120 cm tall.
