A couple of differences between Usnea and Cladonia are: (1) species of Usnea have an open, branching growth form ( a bit like a shrub that has a stem and then numerous branches developing from that one stem) and (2) in Usnea the disk-like structures (apothecia) in which the fungal spores are produced are of much the same colour as the rest of the lichen, whereas in Cladonia the apothecia are often strikingly different - such as the red ones you see here.