2
Southwest Asia, marking the transition of human society from hunter-gatherer to a
sedentary lifestyle (Kilian et al. 2010 ). Triticeae species are also of research interest
due to their potential for crop improvement by understanding and utilization of the
genetic diversity of wild relatives to ensure global food security (Kellogg et al.
1996 ; Mochida and Shinozaki 2013 ). Furthermore, the tribe exhibits a complex
evolutionary history that is not well understood and adds to its appeal for evolution-
ary biologists.
Approximately 80 species of the tribe are diploid, while the majority of species
are allopolyploid , i.e., combining parental genomes from different diploid species
or genera of the tribe. Polyploid species are likely to have originated repeatedly,
involving genetically different parent species and thus resulting in genetically
diverse polyploid species-complexes (Soltis and Soltis 1999 ; Mason-Gamer 2004 ;
Jakob and Blattner 2010 ; Brassac et al. 2012 ). Triticum aestivum is the most promi-
nent allopolyploid species , formed by recurrent hybrid speciation involving three
diploid species of the tribe and thereby combing three related genomes (named A ,
B , and D ) (Petersen et al. 2006 ; Marcussen et al. 2014 ). In Triticeae and in many
other crops, such genomes were defi ned through cytogenetic characterization of
chromosomes together with the analysis of their pairing behavior in interspecifi c
and intergeneric crosses. In comparison to other grass tribes, Triticeae show a low
barrier against hybridization and other introgressive events (i.e., gene fl ow between
different species). This, together with large-scale and small-scale genome duplica-
tions and incomplete lineage sorting of ancestral polymorphisms, results in diverse
genealogical histories for different parts of the genome.
The tribe Triticeae belongs to the Poaceae family and the subfamily of Pooideae.
It is generally accepted to be monophyletic (Watson et al. 1985 ; Kellogg 1989 ;
Soreng et al. 1990 ; Seberg and Frederiksen 2001 ), this means all taxa of the tribe are
derived from a most recent common ancestor. However, the taxonomic treatment of
the tribe’s members continues to be under long-standing debate. Because of its eco-
nomic importance together with the worldwide distribution, it was always of inter-
est to many researchers. Different opinions of taxonomists about the relationships
of taxa, as well as changing methods and perceptions for good classifi catory sys-
tems, resulted in various taxonomic treatments that in several cases led to various
correct scientifi c names for the same taxon. The circumscription of several of the
tribe’s genera is also under debate (e.g., to include the genus Aegilops into Triticum
or to split it into several genera). The most recent description of Triticeae genera and
a discussion of their level of acceptance can be found in Barkworth and von Bothmer
( 2009 ), and is summarized in Table 1.1. Today, there is common consent that a good
classifi cation of a taxonomic unit like Triticeae starts with a thorough evaluation of
phylogenetic relationships , based on analyses of different portions of the genome
and including taxa of all genera or genomic groups and thereby covering their whole
distribution area (Barkworth 2000 ; Mason-Gamer 2005 ; Petersen et al. 2006 ). So
far, there is no study available that resolves the tribe’s evolutionary history in such
a manner that it can be used as a basis for a conclusive taxonomic treatment.
Published studies largely agree, however, that Bromus, the only genus in the tribe
Bromeae, is the sister group to all Triticeae (Kellogg 1992 ; Schneider et al. 2009 )
N. Bernhardt