Pollen, spores, and other plant microfossils are important constituents of Tertiary coals, both as petrographic components (the maceral sporinite) and as distinctive indicators of the nature of the depositional environment in which the coal-forming peat accumulated. Palynological analyses, which have been conducted on Tertiary coals since the 1930's, play an increasingly important role in modern paleoecological analyses of coals.

Among the most important factors controlling the petrographic composition and facies characteristics of coal deposits are the types and relative abundances of plants that composed the peat. At present, wetland environments in which peat accumulates (mires) range from marshes and bogs to forested swamps; each is inhabited by distinctive plant communities. These plant communities are associated with varied conditions of climate, water depth, chemistry, and nutrient supply, and the floras can be indicative of these conditions. In the Tertiary Period, plant communities of mires were also highly diverse and specialized (especially as compared with those of the Carboniferous). The dominant species in some Paleocene mire floras were gymnosperms, but continuing a trend begun in Late Cretaceous time, angiosperms became increasingly prominent through the Tertiary. The diverse: angiosperm-dominated mire floras produced coals that vary significantly in facies and hence in quality. Such contrasts are evident in contemporaneous coals from different paleolatitudes, as well as among, coals of different ages within the Tertiary, as exemplified by selected deposits in the western United. States. The palynofloras of these coals reflect the floristic composition of the plant communities of the ancient mires.