Chloroplast DNA restriction site data support a narrowed interpretation ofEupatorium (Asteraceae)

Chloroplast DNA (cpDNA) restriction site analysis was used to assess relati onships among samples of Eupatorieae from eastern North America. A total of 270 cpDNA variants was recorded from 35 species using 13 restriction enzym es. Phylogenetic analysis using Galinsoga, Flaveria, and Helianthinae as ou tgroups indicated that samples of Ageratina, Hofmeisteria, Mikania, and Ste via, each of which have relatively high base chromosome numbers, formed an unresolved basal polytomy. The remaining samples examined formed a well-sup ported clade, within which there was a split between Brickellia, which has x = 9, and a number of genera with x = 10. Within the x = 10 clade, there w as an unresolved trichotomy, with one group of Ageratum, Conoclinium, Fleis chmannia, and Critonia, a second of Liatris and Trilisa, and a third of Eup atorium s.s. Within the Eupatorium s.s. clade there were three further clad es, with E. sect. Verticillata diverging first, and a subsequent split betw een species originating from North America and those from Asia. The cpDNA r estriction site data provided support for a relatively narrow interpretatio n of Eupatorium, and indicated that a high chromosome base number is plesio morphic for Eupatorieae.