The Portuguese Oak (Quercus faginea) is one of a handful of oak tree species that are native to the Iberian peninsula. It can often be found in close proximity to other Oak species such as the Holm Oak (Quercus ilex), the Cork Oak (Quercus suber), the Pyrenean Oak (Quercus pyrenaica) or the English Oak (Quercus robur). The leaves of the Portuguese Oak are somewhat similar to those of the English Oak, measuring about 4 inches on length with dentate margins and a dark green color when mature. Their shape tends to be slightly spatulate and they have a pinnate venation.
The bark of this oak is quite a bit different from either the Cork or or the Holm oak which have very distinct barks. The image below gives a pretty good idea of what the bark looks like on a fairly young tree.
It is quite common to see "galls" on this species of oak tree (below). This is not a natural part of the tree but is the result of the tree´s defensive mechanism against foreign objects. In this case they are called "galls" because they are produced when the Gall wasp lays its eggs in the soft bark of a new branch inserting them into a small hole that it makes. The tree senses that a foreign object is present and activates it´s defense mechanism that creates a ball that is about an inch and a quarter in diameter with a hard exterior but a sponge like interior. The Gall wasp larvae grows inside the gall finding nourishment in the sponge/cork like interior until it is ready to bore its way out. This is why almost all galls have a small termite like hole in them.
I got a tip from Gus at http://git-forestry-blog.blogspot.com/ who tells me that the "wasp" responsible for this particular gall is the "Andricus quercustozae". I found the image of this wasp on a French website. It is a tiny little wasp about the size of a match head. Check this link for more images of these galls.