Quercus, Linnaeus, 1753

Elliott, Sara J., Grettenberger, Christen L., Donovan, Michael P., Wilf, Peter, Walter, Robert C. & Merritts, Dorothy J., 2016, Riparian and valley-margin hardwood species of pre-colonial Piedmont forests: A preliminary study of subfossil leaves from White Clay Creek, southeastern Pennsylvania, USA, Palaeontologia Electronica 13 (16), pp. 1-26 : 8-11

Quercus Section Lobatae Loudon, 1830

Figure 5

Material. EMS 425010, EMS 425011 ( Figure 5.1-4, 5.6 ), EMS 425012-425013.

Description. Lobe apices acuminate, angle acute. Inferred major secondary veins craspedodromous; fimbrial vein present, exterior tertiaries looped. Quaternary and higher-order vein fabric random to regular reticulate. Areolation well-developed; freely ending veinlets mostly one-branched. Leaf surface with a few small trichomes on the secondary veins. Stomata randomly oriented, guard cell junctions in T-configuration.

Discussion. These fragments are interpreted as asymmetrical lobe tips with acute apices, fimbrial veins, and marginal irregularities at likely sites of bristle-teeth that were broken off during preservation ( Figure 5.1 ). Only a few, small trichomes persist on the secondary veins ( Figure 5.3, 5.4 ). Stomata are randomly oriented ( Figure 5.2, 5.3 ), and the junction of two guard cells of an individual stoma creates a characteristic T-shape ( Figure 5.5, 5.6 ). These features collectively indicate membership in the red oak group ( Quercus Section Lobatae ) and, in Pennsylvania, exclude the unlobed species Q. phellos (Rhoads and Block, 2007) ; however, species-level identification is not possible. The ten species in the red oak group that are native to Pennsylvania vary widely in their environmental preferences (Rhoads and Block, 2007; United States Department of Agriculture, 2011), and without further resolution, these subfossils do not refine environmental interpretation. With the exception of Q. ilicifolia , a shrub, the Pennsylvania species are trees reaching adult heights of 20 -30 meters (Rhoads and Block, 2007).

Figures

FIGURE 5. Quercus Section Lobatae (Red Oak group). 1, Leaf fragment showing asymmetrical lobe with acute apex, EMS 425011; 2, Abaxial leaf surface of EMS 425011, with randomly oriented stomata; 3, Simple trichome on leaf surface near secondary vein, EMS 425011. 4, Trichomes along a tertiary vein, EMS 425011; 5, Individual stoma of modern Q. rubra from York County, Pennsylvania (collection Y2.3 of Wilf, 1997) showing T-shape junction; 6, Individual stoma of EMS 425011.