Circumscription of theArundinoideae and the taxonomic treatments of its tribes have long been disputed. In the present study, 21 species representing the tribesArundineae, Danthonieae, Cortaderieae, andAristideae were examined for prolamin size heterogeneity and immunological cross-reactivities. The immunmological data were analyzed phenetically and cladistically. Prolamins of species examined were similar in size and size diversity except forPhragmites. Structural similarities as measured by ELISA and immunoblotting were very high among all genera exceptAristida andPhragmites. Based on prolamin structure,Aristida is not similar to the core genera of theArundinoideae, the remaining genera could not be distinguished as distinct tribes, and theArundinoideae as represented by the taxa tested appeared monophyletic.