title: A portrait of the C4 photosynthetic family on the 50th anniversary of its discovery: species number, evolutionary lineages, and Hall of Fame.
abstract: Fifty years ago, the C4photosynthetic pathway was first characterized. In the subsequent five decades, much has been learned about C4plants, such that it is now possible to place nearly all C4species into their respective evolutionary lineages. Sixty-one independent lineages of C4photosynthesis are identified, with additional, ancillary C4origins possible in 12 of these principal lineages. The lineages produced ~8100 C4species (5044 grasses, 1322 sedges, and 1777 eudicots). Using midpoints of stem and crown node dates in their respective phylogenies, the oldest and most speciose C4lineage is the grass lineage Chloridoideae, estimated to be near 30 million years old. Most C4lineages are estimated to be younger than 15 million years. Older C4lineages tend to be more speciose, while those younger than 7 million years have <43 species each. To further highlight C4photosynthesis for a 50th anniversary snapshot, a Hall of Fame comprised of the 40 most significant C4species is presented. Over the next 50 years, preservation of the Earth's C4diversity is a concern, largely because of habitat loss due to elevated CO2effects, invasive species, and expanded agricultural activities. Ironically, some members of the C4Hall of Fame are leading threats to the natural C4flora due to their association with human activities on landscapes where most C4plants occur.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5R3C6 r.sage@utoronto.ca.
authors.forename: Rowan F
authors.initials: RF
authors.lastname: Sage
mesh_terms: D005075:Biological Evolution; D017753:Ecosystem; D019684:Magnoliopsida; D010788:Photosynthesis
keywords: Biodiversity; C4 Hall of Fame; C4 plants; Cyperaceae; Poaceae.; convergent evolution; photosynthetic evolution