Common Black Cohosh is a perennial rhizomatous forest herb. Its horizontal rhizomes bear numerous adventitious roots on the underside and aerial stems of annual duration on the upper side, along with knobby scars left from aerial stems of previous years. Leaves are alternate, twice or thrice compound in ternate or pinnate patterns, and large—up to 1 m long. Individual leaflet size and shape vary with position in the large compound leaves, with position of a leaf on the stem, and from population to population. Most often leaflets are coarsely serrate, lobed to deeply incised, with a truncate to cuneate base and an acute to acuminate apex; they are 3–10 cm wide and 2–10 cm long. Inflorescences are terminal, held well above the leaves, sparsely branched, and up to about 1 m long, resulting in a total height of robust flowering specimens to 2 m or so; flowering commences at the bottom of each raceme and progresses apically. The white flowers possess 4 or 5 concave sepals about 5 mm long that promptly drop at anthesis. Just above the position occupied by sepals one finds a series of organs that can be interpreted as either petals or staminodes (sterile stamens); these are oblanceolate to oblong, about 3 mm long, and bear a pair of somewhat irregular lobes at the apex. Functional (fertile) stamens are numerous, 55–100 per flower, and form a globelike mass roughly 2.5 cm in diameter; stamens are 8–10 mm long, and each consists of a slender filament supporting two anther sacs of pollen. Usually there is just a single pistil at the center of the flower but, rarely, 2 or 3 may be present. Ovaries are stout and barrel-shaped, arising from a short stipe at the base and capped with a short style and flat stigma. Fruits are dry follicles, 6–9 cm long. During fruit development stigmas become displaced laterally, and transversely oriented veins of the ovary wall become prominent. Seeds are semicircular, with minutely roughened sides, about 2 mm long and are produced in a double row inside the follicle.

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Copyright © 2017 Virginia Native Plant Society. This brochure first appeared in Virginia Native Plant Society Brochure (2017), 1-3

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