||Wang X, Gowik U, Tang H, Bowers JE, Westhoff P, Paterson AH. Comparative genomic analysis of C4 photosynthetic pathway evolution in grasses. Genome Biol. 2009 10(6):R68.PubMed ID19549309
||Christin PA, Besnard G, Samaritani E, Duvall MR, Hodkinson TR, Savolainen V, Salamin N. Oligocene CO2 decline promoted C4 photosynthesis in grasses. Curr Biol. 2008 Jan 8 18(1):37-43PubMed ID18160293
||(Primary source): Researchers inferred a large phylogenetic tree for the grass family and estimated, through Bayesian molecular dating, the ages of the 17 to 18 independent grass C4 lineages. The first transition from C3 to C4 photosynthesis occurred in the Chloridoideae subfamily, 32.0-25.0 Mya.
||The C4 pathway independently appeared at least 50 times during angiosperm evolution [refs 6,7 in Reference].