The middle Miocene Yakima Canyon flora (15.6 Ma) of central Washington state is one of the few Neogene fossil localities with anatomically preserved seed, fruit and vegetative remains. The detailed morphological and anatomical features preserved in these fossils have allowed us to recognize plants at several infrageneric levels, including section, subsection and extant species. Phytogeographic relationships and ecological associations can also be resolved to varying degrees. The presence of Woodwardia virginica (Blechnaceae), essentially identical to the modern Virginia chain fern of eastern North America, illustrates species longevity, well-known among homosporous ferns. Its occurrence with Osmunda wehrii (subgenus Osmunda) and a small onocleoid fern demonstrates that fern community associations in the Miocene were quite similar to those today. Quercus hiholensis is assignable to subgenus Quercus, section Quercus, and represents a white oak with developmental features that suggest annual fruit maturation, a highly derived feature within the genus, was established by the Miocene. Petrified Liquidambar infructescences showing features of section Liquidambar, provide the first evidence of fruit anatomy for this genus that today has a highly disjunct Asian-North American distribution. Conifers present include abundant taxodiaceous remains and Pinus foisyi (subgenus Pinus, section Pinus, subsection Oocarpae), which is most similar to modern California closed cone pines based on leaf and ovulate cone anatomy. In addition to other typical Miocene floristic elements such as Vitaceae, Cornaceae, and Rosaceae, the Yakima flora contains several fruits and seeds (cf. Rhamnaceae, Zygophyllaceae and Lythraceae) that probably represent extinct genera. The Yakima Canyon flora thus documents anatomy for plants of the widespread temperate flora of the middle Miocene during its maximum geographical distribution.

Key words: Liquidambar, Miocene, petrified, Quercus, Woodwardia, Yakima Canyon