Eupatorium torreyanum is a perennial herb from a short root crown; stems to 1.5 m tall, solitary, rough-hairy, unbranched below middle; axils with small tufts of leaves.
Leaves opposite, sometimes in whorls of 3-4, conspicuously 3-veined, margin coarsely toothed.
Flowers dull white, 5 per head, bracteate base about 0.5 cm tall, cylindrical, finely gray-hairy; inflorescence rounded; blooms Aug.-Oct.
Fruit A plumed achene.
Wetland status: NL.
Frequency in New York City: State Threatened species (S2G5)
Habitat: Open uplands.
Notes: According to Flora of North America: “Eupatorium hyssopifolium includes both diploid and polyploid cytotypes and presents a complex situation taxonomically. The diploids are placed here in var. hyssopifolium, which also includes polyploids and is characterized by relatively narrow leaves. Variety laciniatum has broader leaves and molecular data suggest that it arose through hybridization between var. hyssopifolium and E. serotinum; the name E. torreyanum has been applied to plants of similar morphology, but these are hybrid derivatives of E. serotinum and E. mohrii.”
It is mentioned in Gleason and Cronquist under E. hyssopifolium var. laciniatum as being a “stable entity,” but is not treated separately.
USDAPlants gives the image from Britton and Brown without further information: USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner’s Sons, New York. Vol. 3: 358.
Eupatorium torreyanum – Short, is mentioned under E. hyssopifolium in Native Plants of the Carolinas & Georgia (Radford et al. 1968).