This trnL intron derived phylogeny of the Gentianales represents the most extensive and most evenly sampled study of the group, or any angiosperm order for that matter, to date. Past systematic work using morphological and/or molecular sequence data did not effectively resolve interfamilial relationships within the Gentianales. Increased taxon sampling may effectively distribute phylogenetic signal more evenly and thereby improve resolution of the major families at all levels within the order. Roughly 500 accessions were sampled from major tribes of the Strychnaceae, Loganiaceae, Gelsemiaceae, Gentianaceae, Apocynaceae s.l., and Rubiaceae. Members of the Oleaceae, Scrophulariaceae, and more distally related genera were included as outgroups. Apocynaceae s.l. comes out in the most derived position and has a sister group relationship with a clade consisting of Strychnaceae-tribe Strychneae and Loganiaceae s.str. Gelsemiaceae is supported as a distinct family and is unresolved along with Strychnaceae-tribe Antonieae and Rubiaceae. Surprisingly, Gentianaceae is in the basalmost position; it is also the only family (except for tribes Antonieae and Spigelieae in the Strychnaceae) that lack alkaloids. Most of the traditional families in the Gentianales appear to be monophyletic, except for Strychnaceae and Loganiaceae.

Key words: Apocynaceae s.l., Gelsemiaceae, Gentianaceae, Gentianales, Loganiaceae, phylogeny, Rubiaceae, Strychnaceae, trnL intron