Historical climate changes have had a major effect on the distribution and evolution of plant species in the neotropics. What is more controversial is whether relatively recent Pleistocene climatic changes have driven speciation, or whether neotropical species diversity is more ancient. This question is addressed using evolutionary rate analysis of sequence data of nuclear ribosomal internal transcribed spacers in diverse taxa occupying neotropical seasonally dry forests, including Ruprechtia (Polygonaceae), robinioid legumes (Fabaceae), Chaetocalyx and Nissolia (Fabaceae), and Loxopterygium (Anacardiaceae). Species diversifications in these taxa occurred both during and before the Pleistocene in Central America, but were primarily pre-Pleistocene in South America. This indicates plausibility both for models that predict tropical species diversity to be recent and that invoke a role for Pleistocene climatic change, and those that consider it ancient and implicate geological factors such as the Andean orogeny and the closure of the Panama Isthmus. Cladistic vicariance analysis was attempted to identify common factors underlying evolution in these groups. In spite of the similar Mid-Miocene to Pliocene ages of the study taxa, and their high degree of endemism in the different fragments of South American dry forests, the analysis yielded equivocal, non-robust patterns of area relationships.

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Historical climate change and speciation: neotropical seasonally dry forest plants show patterns of both Tertiary and Quaternary diversification

Using phytolith assemblages to reconstruct the origin and spread of grass-dominated habitats in the great plains of North America during the late Eocene to early Miocene

Neogene paleosols of the Great Plains and central Oregon provide abundant evidence of grasslands of the past. The characteristic surface horizon (mollic epipedon) of grassland soils (Mollisols) can be recognized in paleosols from granular ped structure, abundant fine root traces, dark color, and common carbonate or other easily weatherable minerals. The fossil record of such soils indicates a three-stage evolution of grasslands. Eocene to Oligocene rangelands are represented by paleosols with near-mollic soil structure and fine root traces similar to soils of modern desert grasslands with scattered bunch grasses and shrubs. Paleosols with mollic epipedon and shallow (less than 40 cm down into the profile) calcic horizons are evidence for the appearance of sod-forming short grasslands during the early to middle Miocene. Mollic paleosols with deeper (some 1 m or more) calcic horizons represent tall grasslands and have not been found older than late Miocene. Early stages in the evolution of grassland soils correspond to climatic coolings near the end of the Eocene and middle Miocene. The best understood climatic cooling and drying during the late Miocene (Messinian or 5-7 Ma) is synchronous with the expansion of tall C 4 grasslands.

Neogene expansion of the North American prairie

Morphological data and sequences from the nuclear ribosomal ITS region, and the chloroplast trnL intron and matK locus were sampled from robinioid legumes to infer phylogenetic relationships. The monophyletic robinioid clade includes 11 genetically and often morphologically distinct subclades ranked as genera with the following well supported higher level relationships: ((Hebestigma, Lennea), ((Gliricidia, Poitea), (Olneya, Robinia, Poissonia, Coursetia, Peteria, Genistidium, and Sphinctospermum))). In order to render all 11 robinioid genera monophyletic, the genus Hybosema is synonymized with Gliricidia, and the genus Poissonia is resurrected to accommodate four morphologically disparate species previously classified in Coursetia. Three new combinations are required to accommodate these two generic recircumscriptions: Gliricidia robustum, Poissonia heterantha, and Poissonia weberbaueri. Ages of clades and evolutionary substitution rates are derived from a rate-smoothed Bayesian likelihood approa...

https://www.public.asu.edu/~mfwojci/pdfs/LavinetalSYSBOT2003.pdf

Phylogeny of Robinioid Legumes (Fabaceae) Revisited: Coursetia and Gliricidia Recircumscribed, and a Biogeographical Appraisal of the Caribbean Endemics

https://dspace.library.uu.nl/bitstream/handle/1874/31608/Review%20of%20Palaeobotany%20and%20Palynology%20124%20(2003)%201-2.pdf;sequence=1

J. Landon

Papers

Late Eocene (Chadronian) dicotyledonous woods from Nebraska: evolutionary and ecological significance