Isothecium myosuroides, commonly known as tree moss, is a true moss

Bryidae

Bryidae is an important subclass of Bryopsida. It is common throughout the whole world. Members have a double peristome with alternating tooth segments.-Classification:The classification of the Bryidae.Superorder: Bryanae...

 that grows abundantly on both rocks and trees. It is native to Eastern North America.
It grows preferentially on Angiosperms rather than on conifers because of the manner in which the former take in water creating an ideal moist habitat for the moss to grow on, and because many trees in the flowering plant families are less acidic than coniferous species of trees. I. myosuroides also can grow on rocks.