M. subsimilis has a small to medium sized, foliose thallus measuring 2 to 6 cm across. The thallus lobes are narrow (1 to 2mm wide) and hollow. The upper surface is pale gray to pale greenish gray with scattered rounded perforations while the lower surce is largely black with some browning at the edges. Asexual soredia are produced on short erect lobes and the sexual apothecia do form, though rarely.
The distribtution of M. subsimilis throughout the Pacific Northwest of the United States runs from the northern bound in Alaska and stretches south to California and remains west of the Cascade mountain range.
M. subsimilis is found on hardwood trees and shrubs, especially the trunk of Alnus rubra or red alder, in oceanic forests and riparian areas. The species is a common occurance in the Coast range of Oregon and is often found scattered on the western slope of the Cascade Mountian range.
The perforations on the upper surface of the thallus are distinct characteristics of the genus, separating it from the similar genus Hypogymnia. At one time, M. subsimilis was lumped with M. terrebrata but has been distinguised by differences seen in the soralia.
Brodo, I.M., S.D. Sharnoff and S. Sharnoff (2001) Lichens of North America. Yale University Press, New Haven, Connecticut.
McCune, B. and L. Geiser (2009) Macrolichens of the Pacific Northwest. Oregon State University Press, Corvallis, Oregon.