How big does something have to be to be considered a giant? I guess it needs to tower over its relatives? Well, giant fescue (Festuca gigantea) grows to around 1.5m whereas tall fescue tops that at 2.0m. Still, English common names are often misleading and 1.5m or five feet tall is pretty gigantic compared to many grasses.
Superficially giant and tall fescues are similar in structure but the florescence of giant fescue opens out in to a lovely spray of almost oat-like hairy florets. Close inspection reveals various differences between these two species and the experts will tell them apart readily. For me, though, it comes down to the fact that tall fescue is a plant of grasslands and is also frequently in sunny hedgerows whereas giant fescue prefers shady places like woods and the dark side of hedges. This difference in habitat preference is not a total clincher but it is a good start!
Recent research has indicated that this may not actually be a member of the fescue family and there is some debate as to where it actually belongs in the general scheme of all things grass-like!