Natural History Mushrooms in Winter 13 December 2019 Ian Alexander Pleurotus ostreatus var columbinus: the Winter variety of the Oyster Mushroom. It grows on dead wood, and has a thick, short, often nearly horizontal stem, very tough and elastic, ridged with the gills running down the stem (like a Chanterelle or Funnel). Whereas the top of the usual Oyster mushroom is pale grey-brown, this variety has a handsome blue-grey cap.