Ageratina altissima

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Ageratina altissima, photo by J. C. Lucier (


Ageratina altissima influorescence - from

Taxonomy and Systematics

Kingdom: Plantae

Subkingdom: Tracheobionta (Vascular plants)

Division: Magnoliophyta (Angiosperms)

Class: Magnoliopsida (Dicots)

Subclass: Asteridae

Order: Asterales

Family: Asteraceae

Genus: Ageratina Spach.

Notes on taxonomy: This species was designated as Eupatorium altissimum by Linnaeus in 1753. In 1841, the French botanist Edward Spach first suggested the separation of the Ageratina genus from the Eupatorium. The current name was given in 1970 by R. M. King and H. Robinson.

Although species of Ageratina bear a close superficial resemblance to species in the Eupatorium genus, genetic evidence suggest that they are not nearly as closely related as they appear.

Species of the Ageratina can be visually distinguished from Eupatorium by the imbrication or layering of the latter's involucral bracts into two or three series -- Ageratina bracts are in a single layer.

Descriptive notes

A. altissima (White snakeroot) is a composite bearing flowers in clustered heads. Receptacles contain eight or more white flowers with white, lobed and sparsely short-villous corollas. Leaves are opposite and petiolate, with deltate-ovate to ovate-lanceolate shape, and coarse, doubly serrate margins. Stems are ascending to erect.

As mentioned above, A. altissima can be distinguished from the similar looking Eupatorium by the number of layers of involucral bracts - A. altissima has one while Eupatoriums had two or three). Another distinguishing factor is habitat; Eupatorium are usually found growing in wet, open areas, while A. altissima grows in the shaded understory. Finally, the white-flowering E. perfoliatum which most resembles A. altissima, has, as the name suggests, distinctive, perfoliate leaves which are not found on the Ageratina.

Campus distribution and habitat

Found in high shade areas in forest undergrowth. Specimens were found specifically along the blue trail.

General distribution

A. altissima distribution - from

Grows throughout eastern half of the country, although it is not present in parts of coastal Maine. A. altissima is the only species of the genus found in upper New England, with A. aromatica growing in Connecticut and Eastern Massachusetts.

Other notes

White snakeroot is poisonous. Poison can be transmitted through the ingestion of the milk or meat of cattle that have eaten the plant. The resulting illness is called "milk sickness" and was responsible for the deaths of many early settlers.

Other resources


  • Magee, Dennis W. and Harry E. Ahles. Flora of the Northeast: A Manual of the Vascular Flora of New England and Adjacent New York. Amherst: University of Massachusetts Press, 2007.

External links