Oyster Mushroom?

Oyster Mushroom?

Observation - Oyster Mushroom?. Description: I'm pretty confident these are a type of Oyster fungi, growing on what I think is an Alder Buckthorn but I'm not entirely sure it's Pleurotus ostreatus. I initially thought it was Branching Oyster (Pleurotus cornucopiae) but according to Roger Phillips,

I'm pretty confident these are a type of Oyster fungi, growing on what I think is an Alder Buckthorn but I'm not entirely sure it's Pleurotus ostreatus. I initially thought it was Branching Oyster (Pleurotus cornucopiae) but according to Roger Phillips, it's the wrong time of year for that (not necessarily relevant in Devon!). Based on the size of the caps it might also be Pale Oyster (Pleurotus pulmonarius).

Expert opinion welcome.