Riparian and valley-margin hardwood species of pre-colonial Piedmont forests: A preliminary study of subfossil leaves from White Clay Creek, southeastern Pennsylvania, USA Elliott, Sara J. Grettenberger, Christen L. Donovan, Michael P. Wilf, Peter Walter, Robert C. Merritts, Dorothy J. Palaeontologia Electronica 2016 2016-01-31 13 16 1 26 8W2YL Linnaeus 1753 [245,346,912,937] Magnoliopsida Fagaceae Quercus Plantae Fagales 10 11 Tracheophyta genus   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 Pennsylvaniawithin the white oak group (  QuercusSection  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 Pennsylvaniaand occur within a broad range of environments (Rhoads and Block, 2007; United StatesDepartment 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 StatesDepartment 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 StatesDepartment of Agriculture, 2011), as well as their wetland indicator statuses (Rhoads and Block, 2007; United StatesDepartment of Agriculture, 2011). Therefore, no environmental interpretations were based on these subfossils.