Phylogenetic analysis of molecular sequence data from two non-coding sources (nuclear ribosomal its1+2, and the intron and spacer from the chloroplast trnL-trnF region) strongly supports monophyly of a lineage that coincides with Bremekamp’s Justicieae. Comprising about 1/3 of all species of Acanthaceae, this is the largest and perhaps most difficult of the family’s major lineages; generic limits have been unsettled and classifications above the genus level have not won wide acceptance. Our molecular sequence data provide strong evidence for the existence of several lineages within Justicieae and for relationships among them. Lineages are: (1) Justicia s.l., including New and Old World plants with a rugula (Justicia, Poikilacanthus, Megaskepasma), (2) the Dicliptera lineage, including New and Old World taxa with resupinate corollas and inflorescences consisting of cymule units, (3) the Henrya lineage which comprises a large group of New World taxa with n=18, (4) genera with two monothecous stamens (Razisea, Stenostephanus), and (5) genera with two bithecous stamens + two staminodes and n=21 (Odontonema, Pseuderanthemum). These five lineages are related as follows: ((((1+2) 3) 4 ) 5). Sampling of taxa with four anthers remains inadequate but Asystasia may be basal to other Justicieae. This phylogenetic hypothesis permits examination of a number of morphological characteristics, many of which support this hypothesis. In contrast, tricolporate, hexapseudocolpate pollen do not appear to mark a monophyletic group and instead may be primitive for Justicieae. Also noteworthy is that these results indicate that morphological diversification and speciation within Justicia s.l. have yielded at least 700 species but have taken place with very little molecular evolution at these loci. This raises a number of issues about rates of speciation and molecular evolution, and ages of different lineages within Acanthaceae.

Key words: Acanthaceae, Justicieae, nr-its, phylogenetics, trnL-trnF