13questions unanswered. These studies considered only diploid taxa, with rarely
more than one accession per species and only a small part or biased fractions of the
genome (Hsiao et al. 1995 ; Petersen and Seberg 1997 ; Petersen and Seberg 2000 ;
Petersen 2002 ; Escobar et al. 2011 ). Although not including all diploid genera,
Escobar et al. ( 2011 ) have to date published the most comprehensive multigenic
data set including one chloroplast and 26 nuclear loci, most of which are probably
located on a single chromosome. This study resulted in the recognition of up to fi ve
major clades in diploid Triticeae and agrees with other studies, for instance in the
basal positions of Psathyrostachys and Hordeum in the phylogenetic trees.
Furthermore, it pinpoints clades that are particularly affected by reticulate evolu-
tion or incomplete lineage sorting (e.g., Aegilops , Dasyprum , Secale , and Triticum ).
Recently, the advent of methods that retrieve sequence information from many
different portions of the genome for many accessions and species group(s) under
study at the same time (e.g., methods that make use of restriction-site-associated
differences or aim for the targeted enrichment of genomic parts; for review see
Lemmon and Lemmon 2013 ) coupled with high-throughput sequencing platforms
(e.g., Illumina or Ion Torrent) allow new analysis approaches (Brassac and Blattner
2015). This offers new possibilities for a taxonomically complex group, like that of
the grass tribe Triticeae, and will hopefully result in more robust phylogenetic data
to be used for taxonomic decision-making in the near future.
1.10 Triticeae Taxonomy: Is It Intractable?
After several decades of intense research into Triticeae taxonomy, there is still no
general agreement on a good classifi catory system for the tribe. The reasons for this
are multifaceted. Once a good understanding for the evolutionary history among
monogenomic units is obtained, this information can be used to unravel the relation-
ships among heterogenomic taxa. A conclusive taxonomic treatment for monoge-
nomic and heterogenomic taxa should be based on integrating all available data
from different science disciplines as well as sequence information from different
portions of the genome for a representative sampling of taxa. Though still quite
cost-intensive, newly available DNA sequencing techniques allow for the genera-
tion of such data. Nevertheless, the handling and interpretation of this data will be
very demanding due to the highly reticulate evolutionary processes in Triticeae
together with the presence of paralogous loci caused by large- and small-scale
duplications within genomes. Many incongruent gene trees, that depict the truly
different histories of the genomic fractions under study, are to be expected. An aver-
age phylogeny , true for most parts of the genomes, and associated alternative phy-
logenies, will be necessary to represent relationships within the tribe. New insights
into the tribe’s evolutionary history can mark the starting point for a generally
accepted taxonomic treatment. Still, assuming all taxonomists working on the tribe
could be convinced to follow the same treatment , the achievement of reaching an
agreement on a single accepted name for a certain taxon would be extremely
1 Taxonomic Treatments of Triticeae and the Wheat Genus Tr it icu m