The genus Ixophorus (Paniceae: Poaceae) has a set of morphological characters that suggest relationships to disparate genera in the grass tribe Paniceae. The bristles in the inflorescence imply a connection to Setaria, whereas the mucronate lemma and unilateral primary inflorescence branches imply a connection to Urochloa, and the enlarged lower palea suggests a relationship with some species of Panicum. We have undertaken studies of molecular phylogeny and developmental morphology to investigate the placement of Ixophorus and the developmental basis of its distinctive combination of characters. Sequence data from the chloroplast genes ndhF and trnL strongly support the placement of Ixophorus within a monophyletic ‘bristle clade’, and specifically, closely allied to Setaria. We have documented the development of inflorescences, from the vegetative stage through fully developed spikelets, using Scanning Electron Microscopy (SEM). Variations on themes of branching pattern and primordium differentiation are compared and contrasted to those in Setaria. This enables us to characterize precisely at which stages Ixophorus is developing in a way typical of Setaria, and at what points it is displaying unique developmental patterns. Integrating molecular phylogenetics with SEM data enables us to make more precise statements regarding the morphological variation we use in taxonomy. In this case, our taxonomic product will be a monograph of Ixophorus, which will include this particularly rigorous assessment of its morphology.

Key words: developmental evolution, Ixophorus, molecular phylogenetics, Poaceae