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A plant microfossil assemblage of 24 identified and five unknown pollen and spore types is reported from the early Miocene La Quinta Formation near Simojovel, Chiapas, Mexico. The taxa group into seven paleocommunities representing versions of the modern mangroves (Pelliciera, Rhizophora), swamp and lowland riparian forest (Ceratopteris, Crudia, Pachira), tropical rain forest (Selaginella, cf. Antrophyum, Pteris, Sphaeropteris/Trichipteris, cf. Aguiaria, Crudia, Guarea, Pachira), lower montane rain forest (Alfaroal/Oreomunnea, possibly Eugenia), evergreen cloud forest [Picea, Pinus, Podocarpus, Ericaceae (possibly Cavendishia/Vaccinium)], evergreen seasonal forest (Hymenaea, Ilex, possibly Eugenia), and tropical deciduous forest (Cedrela). Elements of arid and high-elevation habitats were absent or few, and northern temperate elements (Picea, Pinus?) were few or rare. Paleoelevations are estimated at 1000-1200 m (present average 2000 m, maximum 3004 m), MAT (mean annual temperature) at least as warm as the present 24 degrees C, and annual rainfall near the present similar to 2500 mm but more evenly distributed. The La Quinta (Simojovel) and other Tertiary floras from the region reflect a trend toward higher altitudes, more seasonal rainfall, cooling tempertures, increased introduction of cool-temperate elements from the north after similar to 15 Ma (million years), and increased introduction of tropical elements from the south after completion of the isthmian land bridge similar to 3.5 Ma ago.