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 : 11

Quercus Section Quercus Linnaeus, 1753

Figure 6

Material. EMS 425006-425007, EMS 425008 ( Figure 6.2 ), EMS 425009.

Description. Acute, retuse, lobe apices. Primary venation not preserved. Inferred major secondary vein craspedodromous. Fimbrial vein present. Exterior tertiary veins looped or terminating at margin. Quaternary to 6 th- order vein fabric irregular reticulate.

Discussion. These fragments are characterized by an entire margin with a fimbrial vein, and a retuse, asymmetrical lobe apex ( Figure 6.1 ). Secondary veins terminate at the lobe apex, and exterior tertiary veins are looped with inconsistent vein angles. Trichomes are uncommon but can be seen scattered across the leaf surface. Species native to Pennsylvania within the white oak group ( Quercus Section Quercus ) generally have rounded lobe apices, distinguishing them from the bristle-tipped red oak group (Q. Section Lobatae ; Rhoads and Block, 2007). The subfossil specimens are inferred from their preserved venation asymmetry to represent rounded lobe apices, indicating both that they belong to the white oak group and that they cannot be Q. muhlenbergii (Chinkapin Oak) , which is toothed and unlobed or shallow-lobed (Rhoads and Block, 2007). The apparently glabrous leaf surface suggests that the fragments may represent Q. alba (White Oak) , however, due to the small amount of tissue preserved, the specimens cannot definitively be identified to species level.

Seven species within the white oak group are native to Pennsylvania and occur within a broad range of environments (Rhoads and Block, 2007; United States Department of Agriculture, 2011). The majority of species, including Quercus alba (White Oak) , Q. macrocarpa (Bur Oak) , Q. stellata (Post Oak) , Q. prinoides (Dwarf Chestnut Oak) , Q. muhlenbergii (Chinkapin Oak) and Q. montana (Chestnut Oak) , are generally found in non-wetland communities such as hill slopes, ridges, and dry to moist woodlands (Rhoads and Block 2007; United States Department of Agriculture, 2011). However, Swamp White Oak ( Quercus bicolor ), has a similar leaf morphology to the non-wetland species, but occurs in very different habitats, being frequently found along rivers, on the edges of swamps, and in forested wetlands (Snyder, 1992).

With the exception of Q. prinoides , which is usually a shrub, white oak group species are trees growing to approximately 20-30 meters in height (Rhoads and Block, 2007). These species vary in their tolerance to shade, salinity, and fire ( United States Department of Agriculture, 2011), as well as their wetland indicator statuses (Rhoads and Block, 2007; United States Department of Agriculture, 2011). Therefore, no environmental interpretations were based on these subfossils.

Figures

FIGURE 6. Quercus Section Quercus (White Oak group). 1, Lobe of modern Q. alba from York County Pennsylvania (collection of Wilf, 1997); 2, Subfossil, EMS 425008, showing entire margin with fimbrial vein and retuse, asymmetrical apex.