L. H. Bailey Hortorium, 462 Mann Library, Cornell University, Ithaca, New York 14853-4301.
Am J Bot. 1999 Mar;86(3):307-25.
The first reported petrified acorns to show internal anatomical structure are here described from Middle Miocene (∼15.6 million years old) chert of the Columbia River Basalt Group in Yakima Canyon, Washington. Quercus hiholensis Borgardt et Pigg sp. nov. is described from anatomical and morphological fruit features, as well as a little recognized anatomical feature, the umbilical complex. Acorns, each comprising a nut and its cupule, are up to 15.3 mm long and 18.8 mm wide with helically arranged, imbricate, tuberculate cupule scales. They show basal aborted ovules, short styles, broad stigmas, and lack grooves in their cotyledons. These characters and the developmental pattern seen in these fossil acorns demonstrate that Q. hiholensis conforms to genus Quercus (Fagaceae), subgenus Quercus, section Quercus (the white oaks). The correspondence of Q. hiholensis to the modern section Quercus reveals that the derived floral and fruit characters that distinguish section Quercus within the genus had evolved by the Middle Miocene.
这里描述了来自华盛顿雅基马峡谷哥伦比亚河玄武岩群中中新世中期（约 1560 万年）燧石的第一批具有内部解剖结构的石化橡子。描述了 Quercus hiholensis Borgardt et Pigg sp. nov.，其特征为解剖学和形态学上的果实特征，以及一个不太被认识的解剖学特征，即脐复合体。橡子每个由坚果和其壳斗组成，长达 15.3 毫米，宽 18.8 毫米，具有螺旋排列、覆瓦状、具瘤的壳斗鳞片。它们显示出基部败育的胚珠、短花柱、宽柱头，以及子叶中没有凹槽。这些特征以及在这些化石橡子中看到的发育模式表明，Q. hiholensis 符合栎属（壳斗科）、栎亚属、栎属（白栎）。Q. hiholensis 与现代栎属的对应关系表明，在属内区分栎属的衍生花部和果实特征已经在中新世中期进化而来。
