Here it is at last, one of the greatest organisms in the land: English Oak, Pedunculate Oak; Quercus robur. (Curiously it is also known as French Oak!) The term pedunculate comes from the fact that the acorns are borne on stalks, unlike the other native oak, Q. petraea, on which they grow attached directly to the twig (giving rise to its common name of Sessile Oak.)
There are lots of species in the genus Quercus, but this is the type species. It is one of our longest lived plants. The UK has an unusually high number of ancient oaks compared with other European countries. One of the highlights of my natural history peregrinations was being shown around the ancient oaks of Staverton Park by the late, great Prof Oliver Rackham.
An ancient oak can support more insects than any other plant, with more than 400 recorded.
Our oaks are in a bit of trouble from diseases such as Phytophthera and Acute Oak Decline. Prof Rackham was also of the opinion that oaks had stopped self-seeding successfully in woodlands, although whether this was due to deer or disease he wasn't sure.
The oldest trees have all been pollarded. Some are more than a 1000 years old. Old trees often look to be dying but in fact remain alive for hundreds or years. In such states they are at their ecological peak.