CERROS-TLATILPA, ROSA* and J. TRAVIS COLUMBUS. Rancho Santa Ana Botanic Garden. 1500 North College Ave. Claremont, CA 91711. - Phylogenetics of Aristida (Gramineae) based on internal transcribed spacer sequences (nrDNA).
Aristida is one of three genera in the grass tribe Aristideae
along with Sartidia and Stipagrostis. Composed of ca.
330–360 species, Aristida is distributed in the tropics and
subtropics, growing mostly on grassy plains, arid lands, and open
ground. Studies of this taxonomically difficult genus have relied
primarily on morphology, anatomy, and karyology. Taxonomic groupings
have been based principally on inflorescence architecture and awn
characters. Henrard (1926, 1929) recognized seven sections within the
genus. Since Henrard’s contributions little revisionary work has been
done. Towards an improved understanding of the relationships and
evolution of Aristida, we are gathering data from
macromorphology, lemma micromorphology, leaf blade anatomy, and the
nuclear (internal transcribed spacers; ITS) and chloroplast
(trnT-L-F region) genomes. All of the sections of
Aristida and as well as the related genera are being sampled
and, as well, one or a few of the problematic species complexes in
North America (e.g., the A. purpurea complex) are being
targeted. The overarching goal of this research is to test the
existing taxonomic circumscriptions and gain insight into character
evolution, phytogeography, and ecology of this widespread and diverse
genus. Sequences from the ITS region of 34 New World species of
Aristida have proven sufficiently variable for phylogenetic
inference. Three of Henrard's sections are not monophyletic. However,
some species complexes centered around A. adscensionis and
A. purpurea are well supported by bootstrap analysis.
Additional sampling of taxa from different sections of the genus
Aristida, as well as Sartidia, and Stipagrostis,
should provide much better resolution and confidence in the
phylogenies and provide a better overview of the relationships within
this group.
Key words: Aristida, Gramineae, internal transcribed spacers (ITS), phylogenetics