Fungi come in all shapes and sizes - identifying individual species correctly can be tricky.
Many species vary in appearance with age, which often makes them even harder to distinguish.
However, some older fungi (like the one below) develop characteristics that actually make them easier to identify.
Oak Hill Woods Nature Reserve - 16 September 2020
Appearing to sprout from the moss on this fallen log, these Lumpy Brackets
(Trametes gibbosa) have turned from white/grey to green due to algal growth - a fairly common symptom of old age in this species.
Aside from ageing beautifully, this fungus also causes white rot.
Other species are fairly recognisable at any stage of their lives (like the two below).
Oak Hill Woods Nature Reserve - 16 September 2020
These are both examples of King Alfred's cakes fungus (Daldinia concentrica)
(or 'Coal cakes'), and are both very easily identified - despite the second one being visibly older.