HISER, KENNETH M.*, ANDREW N. DOUST, and ELIZABETH A. KELLOGG. Department of Biology, University of Missouri-St. Louis, 8001 Natural Bridge Rd., St. Louis, MO 63121.. - Inflorescence development and phylogenetic relationships of the genus Ixophorus.
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