Rhexophyllum is a medium-sized moss with a distinctive blackish green to reddish green coloration. Its stems have both a central stand and a hyalodermis. The leaves in Rhexophyllum are lanceolate, wide-spreading to squarrose from a weakly clasping base when wet, somewhat fragile, and have margins recurved below but dentate to erose-dentate above. Although the leaf margins are unistratose, the laminae are irregularly bistratose in streaks. Other distinctive features of the genus include its strongly differentiated and sheathing perichaetial leaves and its eperistomate capsules.

In a number of features, such as plant size, stem hyalodermis, leaf shape, sheathing perichaetial leaves, and erose-dentate leaf margins, Rhexophyllum is similar to Leptodontium. It differs from that genus in having a stem central strand, irregularly bistratose laminae and eperistomate capsules. Zander (1993) placed Rhexophyllum in the Bryoerythrophylleae near Mironia and Bryoerythrophyllum. Both genera differ from Rhexophyllum in having a stem sclerodermis.  Bryoerythrophyllum also differs in having unistratose leaf laminae, while Mironia differs in having bistratose leaf margins.