The blue oyster mushroom grows in large clusters and takes on the typical shelf like shape of the Pleurotus species.
The size and shape can vary immensely depending on the growing conditions. Blue Oyster mushrooms required a extremely high level of fresh air exchange, more so than any other mushroom commonly cultivated.
Grown in a high CO2 environment, the Blue Oyster mushroom will have a long and thick stems with small caps.
They also have a huge spore load, which can quickly fill your grow room with a thick spore load.
The mushroom clusters start out with deep blue coloring and eventually turn grey as they age. The fruit is usually thick and meaty and very versatile for culinary uses.
Reference : https://learn.freshcap.com/growing/candidates-for-cultivation-the-blue-oyster-mushroom/