1.4 Conventional Taxonomy
In addition to the subgenera, tribes have been described to accommodate outlying
genera. The composition of genera within subfamilies and tribes has been problematic.
Intergeneric hybridization occurs within these groups. Species definitions are
extended to account for apomixis or hybridization. Some treatments have suggested
that some of the subfamilies have familial status (Hutchinson, 1964); others overlook
subfamilies and worked solely with tribes (GRIN, 2007).