Table 32

Divergence	~ Million years ago
Earliest land plant fossils	420
Origin of angiosperms	200-340
Monocot-dicot divergence	160-240
Origin of grass family	65-100
Oldest known grass fossils	50-70
Divergence of the subfamilies	50-80
Pooideae (wheat, barley, oat)
Bambusoideae (rice)
Panicoideae (maize, sorghum)
Earliest fossil of the rice lineage	40
Divergence of maize and sorghum lineages	15-20
Divergence of wheat and barley lineages	10-14
Divergence of wheat and rye lineages	7

Note:

Panicoideae diverged from the Pooideae-Bambusoideae first, followed shortly by divergence of the latter two subfamilies, or authors suggest that either the Pooideae or the Bambusoideae branched off first. In general, it seems that all 3 subfamilies diverged about the same time. Some phylogenies divide Bambusoideae into two subfamilies, Oryzoideae and Bambusoideae.

Recently, it was found that the gene, Hm1 (in maize), is present in all grasses since shortly after their evolutionary origin and protects them from the fungus Cochliobolus carbonum Race 1 (CCR1), PNAS, USA 105: 1762-1767 (2008)

TABLE 32: About the evolution of Triticeae