PIGG, KATHLEEN B.* AND MARIA TCHEREPOVA. Department of Plant Biology, Arizona State University, Box 871601, Tempe, AZ 85287-1601. - Taxonomic, phytogeographic and ecological significance of the Yakima Canyon flora (middle Miocene, Washington state, USA).
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