Dendrolycopodium dendroideum spreads by subterranean horizontal stems, each upright shoot appearing somewhat like a small individual tree. The lateral branches are essentially round, not conspicuously flattened as in D. obscurum. Leaves on the main stem are clearly spreading. The leaves along the lower surface of the branch are about the same size as the other leaves.

Dendrolycopodium hickeyi and D. dendroideum were long considered to be varieties of D. obscurum and the three species can be difficult to distinguish, especially in dried specimens. The characters by which they are separated are subtle and careful observation and a little practice are required. Refer to the key. This species was long known as Lycopodium obscurum.