Populations of Sesbania in Hawaii exhibit a classic situation found among many Hawaiian plant taxa in that there is much morphological variation across populations but the variation for any single trait appears as a cline. Such apparent clinal variation has lead to conflicting classifications in Sesbania with from one to seven species being recognized by various workers. We have employed data from isozymes, DNA sequence variation (SSCP of ITS-nrDNA), and morphology in multivariate analyses and phylogenetic analyses to address the following questions: 1) Are populations of Hawaiian Sesbania a monophyletic group? 2) Can the different populations be discriminated from each other multivariately? 3) Do individual populations or groups of populations represent discrete, multiple evolutionary lineages? 4) What are the phylogeographic relationships of populations/taxa? 5) What are the implications of our results for the classification of Hawaiian Sesbania? Preliminary results suggest the following: Hawaiian populations of Sesbania are a monophyletic group; some single populations and some groups of populations are distinct and non-overlapping for various combinations of data and they may represent discrete lineages; the data support the recognition of at least the following taxa, here listed as informal names based on the work of Char: "polihaliensis", "kauensis-intermedia", "manaensis", "tomentosa-Maui", "tomentosa-Hawaii". Even when all populations of Hawaiian Sesbania are treated as a single species, this is a rare taxon. The classification proposed here suggests that Hawaiian Sesbania is a complex of extremely rare and endangered species.

Key words: Fabaceae, Hawaii, Sesbania