Phylogenetic utility of the nuclear rDNA ITS region in subfamily Ixoroideae (Rubiaceae): comparisons with cpDNA rbcL sequence data

ITS of the nrDNA were sequenced for 21 taxa in Ixoroideae and outgroups (Ru biaceae) and compared with sequences of the cp-gene rbcL. Separate and comb ined analyses were performed. ITS-variation was extensive and, because of a lignment ambiguities, some sites were excluded from the analyses. Several t opologies from the rbcL analysis that conflicted with earlier classificatio ns are corroborated by the ITS data: 1) Posoqueria should be excluded from Gardenieae. 2) The disputed genus Bertiera, previously in Gardenieae, is ba sal in an extended Coffeeae, including Tricalysia. 3) Ixora should be exclu ded from Pavetteae. 4) Vangueria, (Antirheoideae), belongs to Ixoroideae. T his affiliation of Antirheoideae tribes with Ixoroideae is also shown by ne w ITS and rbcL data for Alberta. Incongruities found between the two data s ets may be caused by density of taxon sampling, different evolutionary rate s, phylogenetic sorting, homoplasy caused by functional constraints, or sam pling of non-orthologous ITS types.