Black rock-moss (Andreaea rupestris) may easily be confused for a crustose lichen. It forms brittle, crusty rusty red to blackish patches on exposed rock surfaces and look somewhat similar to many crustose lichens.

But with closer examination, you can see distinct stems and leaves.Under the microscope, you can see that the leaves are one-cell layer thick and that the walls of the cells are thick particularly towards the base of the leaves. You can see the cells contain numerous round green chloroplasts that function in photosynthesis.

Near the base of the leaves, the walls are thicker and most cells are dead and lack chloroplasts.

The unusual feature of this moss are the distinct capsules that open by four slits in the capsule wall. Sometimes these plants are called lantern mosses because of the similarity of the capsules to Chinese or Japanese paper lanterns.

 

There are about 100 species of Andreaea in the world of which about 11 species in BC. Andreaea rupestris is by far the most common species. Evolutionary, it is a group of mosses that is very distant from all other mosses and has been placed into its own class, the Andreaeopsida.