Eupatorium perfoliatum
Distinguishing Features: leaves, especially lower ones, are perfoliate; heads have 9-13 flowers.
Habitat: open, wet areas - ditches, edges of ponds and streams.
Geographic Distribution : widespread in eastern U.S., entirely sexual diploids.
Similar Species: Eupatorium resinosum has leaves that sessile rather than perfoliate.
Molecular Data : samples of E. perfoliatum (DNA #s ) differ in the ITS sequence from all other species, which has allowed it to be recognized as the progenitor lineage for hybrids including E. fernaldii and E. novae-angliae
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