Northern Ontario Plant Database
Caulophyllum thalictroides (L.) Michx.
En: blue cohosh
Berberidaceae (Barberry Family)
General: A perennial herb (forb), 3–7.5 dm tall; smooth (glabrous), with a whitish bloom (glaucous); growing from a short, horizontal rhizome.
Leaves: Alternate, with 2 very divided compound leaves; the axis of the lower leaf divided into 3 main branches (ternately compound), each bearing up to 9 short-stalked leaflets. The upper leaf, subtending the inflorescence, is smaller with fewer leaflets. Leaflet blades oblong-obovate, 3–8 cm long, glabrous; green above, paler and glaucous beneath; base rounded; apex divided into 2–3 ovate pointed (acute) to blunt (obtuse) lobes; margins entire.
Flowers: Bisexual, in a terminal cluster (cyme) of several flowers. Sepals 6, petaloid, greenish-yellow to purple, lanceolate, 3–6 mm long; petals 6, yellowish-green, 1–2.5 mm long, nectar-producing (nectariferous), fleshy, rounded, and curved upward at the tip, abruptly narrowed below into a short claw; stamens 6, nearly as long as the petals; pistil 1, with a superior ovary that splits open and shrivels as the 2 enclosed seeds mature. Flowers bloom in late May to early June.
Fruit: Since the ovary of Caulophyllum thalictroides tears open and shrivels before the 2 seeds mature, no true fruit is produced. The seeds are usually mistaken for fruits, however, since the seed coat develops into a fleshy, glaucous, bright blue covering around the globose seeds.
Habitat and Range: Blue cohosh is native to rich deciduous forests in eastern North America. In northern Ontario, it is usually associated with floodplains and low rich woods adjacent to river systems.
Similar Species: The leaves of Thalictrum pubescens (tall meadow rue) and Aquilegia canadensis (wild red columbine) are similar to those of Caulophyllum thalictroides, but the flowers and fruits of each are distinct enough to clarify any initial confusion. Linked images here are from the Gallery of Connecticut Wildflowers, a website of the Connecticut Botanical Society.
Internet Images: The Caulophyllum thalictroides webpage from the Wildflowers of Missouri website. See this link for excellent closeups of blue cohosh flowers at the end of the webpage.
The Caulophyllum thalictroides webpage from the Gallery of Connecticut Wildflowers, a website of the Connecticut Botanical Society.
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