A recent controversy concerns whether plant traits that are assumed to be adaptations to fire originally
evolved in response to selective factors other than fire. We contribute to this debate by investigating the
evolution of the endemic woody flora of the fire-prone Cerrado of central Brazil, the most species-rich savanna
in the world. We review evidence from dated phylogenies and show that Cerrado lineages started to diversify
less than 10 million years ago. These Cerrado lineages are characterized by fire-resistant traits such as thick,
corky bark and root sprouting, which have been considered to have evolved as adaptations to drought or
nutrient-deficient soils. However, the fact that the lineages carrying these features arose coincident with the rise
to dominance of flammable C4 grasses and expansion of the savanna biome worldwide, and postdating the
earlier origin of seasonal climates and the nutrient-poor, acid Cerrado soils suggests that such traits should be
considered as adaptations to fire regimes. The nature of these features as adaptations to fire is further suggested
by their absence or poor development in related lineages found in fire-free environments with similar edaphic
conditions to the Cerrado and by their repeated independent origin in diverse lineages. We present evidence to
demonstrate that the evolutionary barrier to entry to the Cerrado is a weak one, presumably because of the
ease of evolution of the necessary adaptations to fire regimes for lineages inhabiting neighboring fire-free
biomes.
Keywords: adaptive radiation, exaptation, Neotropics, phylogenetic niche conservatism, plant evolution
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