Abstract
The Thunder Mountain paleoflora from the middle Eocene (46–45 Ma) of central Idaho represents an upland flora dominated by conifers. However, because many of the conifer species recognized at Thunder Mountain include a mixture of detached organs from different localities of different ages it is unclear which conifer taxa are present in or absent from the flora. Reexamination of the megaflora suggests Pseudotsuga and Cephalotaxus are equivocal, Thujopsis is not present, and the holotype ovulate cone of Larix leonardii does not show definitive features to justify its placement in Larix. The species Chamaecyparis edwardsii, Picea deweyensis and Abies deweyensis are based on fragmentary organs identifiable only to genus. Pinus baileyi is not closely related to P. longaeva (subgenus Strobus, subsection Balfourianae) but is an excentromucronate hard pine with affinities to members of subgenus Pinus, cf. subsection Pinus. Revision of the Thunder Mountain conifer megafossil assemblage is a step toward clarifying the species present in the flora to provide further understanding of the diversity, evolutionary relationships and phytogeographic history of conifers during the Tertiary.
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