it is dark brown on top, instead of the usual pale beige of Pleurotus pulmonarius (wild and in the shops) and P.ostreatus in the wild which is bluey-grey on top.
This gets variety gets a mention in Arnolds (1990) which was in the late Colin Duke's library.
It is growing on a dead Cordyline stem - killed by frost a few years ago. (Cabbage Palm.)
Reminder fungus foray this Saturday at Stoodley Glen with Halifax Scientific Society. (See bottom of post below.) All welcome. No charge.