Spikelets of S. verticillata (a) showing inflorescence bristles and P. bulbosum (b) lacking bristles. Scale bar (a) = 500 micrometers, (b) = 1000 micrometers.
Emilie Bess
Masters Student
Zionsville, Indiana
BS - University of New Mexico 2001
Research interest: Phylogenetics of Poaceae
I joined the Kellogg lab as a master's student in 2002 in order to investigate some of the unexpected relationships among grass species that have been revealed in the extensive family phylogenies produced in the lab. My thesis project involves refining the placement of two species of Panicum through the use of developmental, morphological, anatomical, molecular, and chromosome data.
My species of interest are Panicum bulbosum, a weedy plant found in the tropics and sub-tropics between Arizona and Ecuador, and Panicum antidotale, a pasture grass that originated in Asia. In investigations of ndhF and trnL chloroplast DNA regions, these two grasses were placed in a group with the genera Setaria, Cenchrus, and Pennisetum, all of which display bristles on the inflorescences. Like all Panicum grasses, P. bulbosum and P. antidotale produce inflorescences that lack bristles, so this placement was a surprise. If these two species really are more closely related to the "bristle clade" grasses than they are to other non-bristle-bearing grasses, they may offer insight into the processes of morphological evolution within Poaceae.
In order to determine where these two species belong, I began with taxonomic work in the Missouri Botanical Garden herbarium. Panicum bulbosum currently represents the synonymy of 5 species and 6 varieties and as a result, is the only member of the section Bulbosa. The morphology of the species varies considerably over its large geographic range, so I measured plants from all parts of the range and planned a collecting trip. In the summer of 2002, I collected P. bulbosum and P. antidotale in central Mexico, Honduras, and the southwestern US. Panicum bulbosum grows most abundantly at high elevations on the steep sides of hills, mountains, and watersheds. I found the plant in cloud forests, high deserts, and on the sides of volcanoes. Because P. antidotale has a metropolitan distribution, I was able to collect it along the way.
The field-collected samples have provided material for molecular sequence analysis, SEM photographs of developing inflorescence structures, chromosome counts, leaf anatomy sections, and additional morphological measurements. Using the trnL and ndhF chloroplast DNA and knotted nuclear DNA sequences, I will be able to place the two species in the molecular phylogenies that have already been produced. The information about inflorescence development will allow for comparison with existing data on the development of "bristle clade" inflorescences. And because P. bulbosum has undergone so many taxonomic changes, the additional information will allow me to complete a taxonomic revision of the species and find it a suitable placement (and likely a new genus) within the Panicoid grasses.