Caulophyllum thalictroides (L.) Michx.

Blue Cohosh

Caulophyllum thalictroides plant2

Family - Berberidaceae

Habit - Rhizomatous perennial herb.

Stems - Ascending to erect, to 60 cm, strongly glaucous, terete, green with purple at the base, glabrous.

Caulophyllum thalictroides stemStem and node.

Leaves - Usually two per stem. Lower leaf 3 times ternately compound, 20-32 cm long, usually sessile, occasionally with a petiole to 4.5 cm long; upper leaf twice ternate, 8.5-14.0 cm long. Leaflets 3(4-5)-lobed at the apex, entire, glabrous, 4-5 cm long, 3 cm broad. Lobes of the leaflets acute, with a small whitish apex. Main veins of the leaflets arising from the base of the leaflet. All veins impressed above, expressed below. Lateral leaflets often oblique at the base.

Caulophyllum thalictroides leafletAdaxial surface of leaf.

Caulophyllum thalictroides leaf2Leaflet abaxial.

Inflorescence - Terminal panicles to 6 cm long, with 4-16 flowers. Peduncle to 3 cm long, glabrous. Each division of the panicle subtended by a minute bract, these 1-2 mm long, acute, scarious on the margins. Flowers immediately subtended by 3-4 sepal-like bractlets.

Caulophyllum thalictroides inflorescence2Inflorescence.

Caulophyllum thalictroides inflorescence3

Flowers - Petaloid sepals 6, yellow-green, spatulate, rounded at the apex, 5 mm long, 2-3 mm broad, with slightly darker veins, distinct. Petals much smaller than the sepals, green, glabrous, hooded, 2 mm long, 2 mm broad at the apex. Stamens 6, ascending. Filaments green, glabrous, 1.5 mm long. Anthers yellow, 1 mm long, 1 mm broad, bi-lobed. Ovary green, obovoid, glabrous, 2 mm long, 2 mm broad, slightly 3-sided, unilocular, with 3 ovules, tapering into a 1 mm long style. Stigma minute. Placentation basal.

Caulophyllum thalictroides bractsBractlets.

Caulophyllum thalictroides flowerFlower.

Caulophyllum thalictroides flower2

Fruits - Fruit wall rupturing early in development to expose the developing seeds. Seeds 1 or 2 per fruit, 6-9 mm long, spherical, each on a thick stalk 4-7 mm long, the seed coat fleshy, blue, glaucous.

Caulophyllum thalictroides fruitsInfructescence.

Caulophyllum thalictroides fruits2Seeds.

Flowering - March - May.

Habitat - Mesic and bottomland forests, rich wooded ravines, north-facing wooded slopes, moist base of bluffs.

Origin - Native to the U.S.

Lookalikes - None.

Other info. - This species can be found scattered throughout most of Missouri but is not particularly common. Its U.S. distribution includes most of the upper Midwest and New England, and also extends into Canada. It is easily identified in the field by its glaucous stems, ternately divided leaves, and yellow-green flowers. If the plants are in fruit, the brilliant blue seeds are unmistakable. The plant is an indicator of relatively undisturbed habitat.

Rootstocks of blue cohosh were used medicinally by Native Americans to treat a variety of ailments, including rheumatism, toothaches, menstrual problems, and various digestive and urinary disorders. It has also been used as an abortifacient. The berrylike seeds are considered poisonous, and the plants can cause skin irritation in some people. The plants contain both alkaloids and saponins, many of which are toxic. The epithet "thalictroides" refers to the resemblance of the leaves to those of plants in the Thalictrum genus (meadow rue).

Photographs taken at Earthquake Hollow Conservation Area, Callaway County, MO., 4-13-04 (DETenaglia); also at Weldon Spring Conservation Area, St. Charles County, MO, 4-17-2016, and Crawford Estate Conservation Area, Clark County, MO, 7-8-2017 (SRTurner).