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Plant microfossils are reported from the late Tertiary Padre Miguel Group and the Pliocene Herreria Formation of southeastern Guatemala. The most abundant palynomorphs are cf. Acrostichum (maximum 45%), Cyperaceae (29%), cf. Antrophyum (27%), monolete fern spores (16%), and Pinus (11%). Pollen grains of Picea, Juglans, Quercus, and Ulmus, primarily from the Padre Miguel flora, reveal the presence of a northern cool-temperate element. The younger Herreria flora is more lowland and warm temperate. In the absence of evidence for substantially higher elevations, the differences between the Neogene and modern vegetation are attributed mostly to climate. MAT (mean annual temperature) is estimated 2 [degrees] - 3 [degrees] C cooler than at present for the Padre Miguel flora, and [approximately]3.5 [degrees] C warmer for the Herreria flora. There is little evidence for arid vegetation, and the tropical rain forest was absent or poorly represented. These data are consistent with those of other fossil floras in the region and with trends suggested by isotopic paleotemperature analysis and global sea-level changes. The Guatemala assemblages further provide evidence that the current version of the tropical rain forest is recent in origin and has undergone considerable change in its range and composition throughout the late Cenozoic. Key words: Guatemala; Neogene; paleocommunities; paleoenvironment.

An assemblage of 17 identified and four unknown pollen and spore types is reported from the Pliocene Rio Banano Formation of southeastern Costa Rica. The most abundant are monolete fern spores, Palmae, cf. Antrophyum, Symphonia, Pelliceria, Lacmella (previously unreported in the fossil record), Alchornea, and Sabicea. These arrange into two paleocommunities - mangroves and lowland tropical rain forest. Annual precipitation is estimated at near the present [approximately]3500 mm, but less seasonal, and the MAT (mean annual temperature) at [approximately]27 [degrees] C. No pollen taxa representing distinctly arid or high-altitude vegetation was being blown or washed into the coastal depositional basin, and no pollen grains were recovered of northern temperate elements that are present in Neogene floras to the north in Guatemala and southeastern Mexico. These data are consistent with those from 12 other Miocene and Pliocene palynofloras from northern Latin America, indicating the late appearance of dry habitats and moderate paleoelevations and a progressive southward introduction of northern temperate elements with late Cenozoic cooling. Key words: Costa Rica; palynoflora; Pliocene.