Umbilicaria americana

Umbilicaria is a rather large genus of lichens usually found attached to rocks that consist of small rounded lobes that are attached at a single point to the rock by a holdfast.

On a recent hike with the Kamloops Hiking Club I found some frosted rock tripe lichen growing amongst mosses on the sheltered north-facing side of a rock outcrop. It was growing intermixed with mosses.

It is somewhat unusual in this genus in that the upper surface is white and powdery in appearance. Most species in this genus are dark brown, grey, or black. It is not a common species but it sometimes occur on more or less sheltered rock surfaces often in association with mosses or other lichens.

The undersurface of the lichen is dark brown to black in appearance and appears to lacks rhizines, small root-like structures that are common on many lichens and help to anchor the lichen thallus to the substrate.

When viewed up close with a handlens, the underside of the dark thallus has a coarse pebbly texture somewhat like coarse sandpaper.