The genus Quercus
(Fagaceae) has 450 species estimated worldwide  and has been widely investigated for years, not only due to their extensive use in the wine and wood industries but also for animal feeding and medicinal purposes .
Stolynoff and Hess (2002) did a survey of the genus Quercus
in Illinois and found the taxonomic confusion of Quercus falcata found in southern Illinois and Quercus ellipsoidalis found in northern Illinois.
What is the common name for a tree of the genus Quercus
In addition, the genus Quercus
presents a very strong affinity for lichens, as shown by [53, 64, 65].
Description of two new species of Dryocosmus (Hymenoptera: Cynipidae: Cynipini) inducing galls on the strictly asian subgenus Cyclobalanopsis of the genus Quercus
, with a key to species of Dryocosmus in East Asia.
All these studies evidence that the intra-generic diversity is intimately related with extended introgression in close species from genus Quercus
(Rushton, 1993; BACILIERI & al, 1996; RIESEBERG, 1997).
The genus Quercus
(the oaks) is characterized by complicated taxonomical patterns (Manos et al., 1999), resulting from frequent parallel or convergent evolution of vegetative characters, pronounced intraspecific variation, low differentiation among closely related species, and hybridization (Tucker, 1974; Hardin, 1975; Aas, 1993; Kleinschmit et al., 1995; Bruschi et al., 2000; Kremer et al., 2002; Bruschi et al., 2003; Gonzalez-Rodriguez et al., 2004; Tovar-Sanchez and Oyama, 2004; Gonzalez-Rodriguez and Oyama, 2005).
Acorns of different oak species (genus Quercus
) have different concentrations of fat and tannin and differences in germination schedules (Table 1; Smallwood et al., 2001).
When it comes to originality, oaks, members of the genus Quercus
, are a perfect example of the possible diversity of margins within a single genus.
Clarification of the relationship between nuclear genetic diversity, chloroplast genetic diversity and species identity in the Lobatae, while beyond the scope of this investigation, could reveal the impact of interspecific hybridization on the origin of species in this speciose section of the genus Quercus
. As all the Lobatae in eastern North America would have retreated south as the glaciers advanced, we argue that our whole tree silvic character criteria are sufficient for the inference postglacial migrations.
A common feature for the three species of Roburocoris, which are known from more than one collecting event, is their apparently rather strict affinity to plants of the genus Quercus
in concert with rather limited specificity to certain species of oaks.
For example, all Oaks belong to the genus Quercus
and have many common characteristics.