Dendrolycopodium obscurum spreads by subterranean horizontal
stems, each upright shoot appearing somewhat like a small individual
tree. The lateral branches appear flattened if viewed from the
end or side. Leaves on the main stem are tightly
appressed. The leaves along the lower surface of the branch
are obviously smaller
than the other leaves.
Dendrolycopodium hickeyi and D. dendroideum were previously
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 previously known as Lycopodium obscurum.