Description: Differences of the most commonly confused Eupatorium's. The inflorescence of Eupatorium purpureum is domed-shaped, while E. maculatum is more flat-topped. E. fistulosum is also domed, but the stem is more purplish throughout, while E. purpureum the purple is mainly at the nodes. Also, the stem of E. fistulosum has a large central cavity, while in E. purpureum it is only slightly hollow . See other Eupatorium photos for more characteristics.