Phylogenetic relationships of the grass family inferred from the sequences of
the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA
(rDNA) are generally in accord with the boundaries of the six commonly
recognised subfamilies: Bambusoideae, Pooideae, Arundinoideae,
Centothecoideae, Chloridoideae and Panicoideae. ITS phylogeny recognises the
herbaceous bamboo allies, Streptochaeta and
Pharus, as the basal taxa to all grasses. The core grass
lineage is resolved into three major clades: the basal Bambusoideae is sister
to the monophyletic Pooideae and the
Panicoideae–Arundinoideae–Centothecoideae–Chloridoideae
(PACC) clade. Several genera with uncertain taxonomic affinities,
Lygeum, Nardus,
Brachyelytrum, Diarrhena,
Anisopogon, Ampelodesmos, and the
tribe Stipeae, are all clustered with a broadly defined Pooideae, and may be
the ‘missing links’ between the Pooideae and the Bambusoideae.
Relationships of the PACC clade indicate that C4
photosynthesis evolved independently among and within the PACC subfamilies.
ITS phylogeny of the grass family, and evidence from the chloroplast genome,
cytogenetics, fossil records, biogeography, and plate tectonic theory, suggest
that the origin of the grasses is probably ‘out of South America’.
DNAbased detection of western gall rust
