Both species of Hypopterygium are dendroid mosses often growing in large clumps.

Hypopterygium didictyon is a common rain forest or wet forest terrestrial or sometimes epiphytic moss. The fronds has an overall glaucous (whitish-greenish) appearance. The leaves are arranged in three ranks such that there is a row of leaves on the shoot underside that is reduced in size and is sometimes referred to as underleaves.

H. tamarisci is rarer and found mostly in the Northeast part of the state. It is distinguished from H. didictyon mostly by microscopic characters.