Tall Thoroughwort (Eupatorium altissimum) in Westminster, MD
Photo of Tall Thoroughwort (Eupatorium altissimum)
The Eupatorium genus has over 30 species in North America, and even in a limited ecoregion like the Northern Piedmont where this plant occurs, there are 19 species. This individual is Tall thoroughwort (Eupatorium altissimum). This species has a strong preference for higher pH soils and also prefers dry conditions, which contrasts with the rest of the genus, most of which prefer wetter conditions. The combination of dry, high pH conditions makes this species much more likely than any other of its genus. In the case where you know that the soil pH in an area is high, this clue can be as useful as morphology. But conversely, when you have definitively ID'ed a plant as this species, it can function as a clue to the soil pH, which may help you to identify other plants on the same site.
