Anatomically Preserved Middle Miocene Flora at Yakima Canyon, Washington State: Floristic Composition, Evolutionary, and Phytogeographic Significance

华盛顿州中部中新世中期的亚基马峡谷植物群（15.6 Ma）含有解剖学上保存完好的种子、果实和营养植物遗迹，这些在北美新近纪是非常罕见的。 这些化石提供了分类学、进化和植物地理学的数据，这些数据是不可能从保存较普遍的新近纪叶压缩植物群中获得的。 根据形态学和解剖学特征，植物可以在不同的属下分类学水平上被识别，包括：一种松树，Pinus foisyi，可归属于Oocarpus亚组，其中包括现存的加州闭锥松;一种橡树，Quercus hiholensis，属于Quercus组，其橡子发育特征与现代白色橡树非常相似;一种枫香树，枫香树，类似于枫香组的几个现代种，在蕨类植物中，主要是现代的狗脊蕨，可能与现代的弗吉尼亚链蕨W. virginica和薇菜Osmunda wehrii，后者属于现代薇菜亚属（Subgenus Osmunda）。 这些植物代表了中生混交林达到最大地理分布的时间间隔，并在可能是新近纪最温暖的时间间隔内生长。在某些情况下，它们代表了广泛多样的温带植物群的“最后一站”，今天的代表是亚洲/北美东部间断分布的植物。进一步的研究将记录第一个温带中新世中期植物群的概述，以解剖学保存的化石遗骸为基础，并存在几个灭绝的中新世属。

ABSTRACT9980388PiggThe middle Miocene Yakima Canyon flora (15.6 Ma) from central Washington state contains anatomically preserved seed, fruit and vegetative plant remains that are quite rarely preserved in the Neogene of North America. These fossils provide taxonomic, evolutionary and phytogeographic data impossible to obtain from the more commonly preserved Neogene leaf compression floras. Based on morphological and anatomical features, plants can be recognized at varying infrageneric taxonomic levels including: a pine, Pinus foisyi, assignable to Subsection Oocarpae, which includes extant California closed cone pines; an oak, Quercus hiholensis of Section Quercus, with acorn developmental features quite similar to those of modern white oaks; a sweet gum, Liquidambar, similar to several modern species of Section Liquidambar, and, among the filicalean ferns, essentially modern Woodwardia, probably assignable to the modern Virginia chain fern W. virginica, and Osmunda wehrii, which fits within the modern Subgenus Osmunda. These plants represent the time interval when the mixed mesophytic forest reached its maximum geographic distribution and grew during what was possibly the warmest interval in the Neogene. In some cases, they represent the "last stand" of a widespread, diverse temperate flora that today is represented by plants with a disjunct Asian/eastern North American distribution. Further study will document an overview of the first temperate middle Miocene flora to be based on anatomically preserved fossil remains, and the presence of several extinct Miocene genera.