4
and that the genera Psathyrostachys and Hordeum diverged early on from the rest of
Triticeae. Aegilops and Triticum are closely related and are of rather recent origin
(Kellogg et al. 1996 ; Petersen and Seberg 1997 ; Mason-Gamer and Kellogg 2000 ;
Escobar et al. 2011 ). Furthermore, it can be assumed that diploid species and
monogenomic taxa (i.e., taxa possessing a single genome type in diploids and poly-
ploids) are the basic units within Triticeae and that heterogenomic polyploids
(mostly intergeneric allopolyploids that combine different genomes in various com-
binations) form a second level of taxonomic entities (Kellogg 1989 ; Seberg and
Frederiksen 2001 ).
The aim of this chapter is to give a short review on the important taxonomic treat-
ments of Triticeae through time (and in more detail on Triticum ), thereby providing
guidance through the multitude of classifi catory systems.
1.2 Short Introduction to Taxonomy, Phylogenetics ,
and Nomenclature
Taxonomy in a broad sense is the theory and practice of identifying, describing, and
classifying organisms into a hierarchical system of taxa (e.g., genera, species, sub-
species), including phylogenetics that uncovers evolutionary relationships among
organisms, and nomenclature, which is how to correctly name an organism.
Taxonomy is not static and its treatments might change whenever new knowledge is
gained that more appropriately refl ects the evolutionary history of taxa. The rational
behind the objective to anchor taxonomy in the evolutionary history of the organ-
isms is the assumption that this, in the long-term, will result in a stable system, as
all taxa should have originated through a single evolutionary process. There is gen-
eral agreement that taxonomic decisions should therefore be made by integrating all
available knowledge from different scientifi c disciplines including morphological,
cytogenetic, and molecular data. This combination of conceptual and methodologi-
cal achievements was described as integrative taxonomy (Padial et al. 2010 ), but
there are no formal rules to follow on how to classify tribes into lower-ranked taxa
(Barkworth and von Bothmer 2009 ). Taxonomist working on the same group of taxa
may disagree on which kind of data, and to what extent that data, should be taken
into account for taxonomic decisions, and if few large or many smaller taxonomic
units should be preferred. Taxonomists may even differ in their opinion regarding
what a species actually is. There are several contemporary and partially confl icting
species concepts. Some might prioritize the phylogenetic species concept in that a
species is the smallest unit for which a monophyly (i.e., a clade comprising an
ancestor and all of its descendants, which is inferred by the possession of shared
derived characteristics, so called synapomorphies) can be found (Rosen 1979 ;
Cracraft 1983 ). Recently, de Queiroz ( 2007 ) proposed a unifying species concept,
based on the common denominator of all concepts. He stated that species are evolu-
tionary lineages independent of other such lineages and that, for instance, crossing
behavior, ecology, and phylogeny are tools to infer such independence of lineages.
N. Bernhardt