Plant of the Week
Frosted rock tripe (Umbilicaria americana Poelt & T. Nash)
By Chantelle DeLay
Umbilicaria americana is a lichen in the family Umbilicariaceae (Kingdom Fungi). Umbilicaria americana is found in North America, up to northern Canada and south to the edge of Mexico. In the United States, it occurs mostly from eastern Washington to western Montana, from southwestern Arizona to northern Colorado, and around the northern Great Lake states.
This species is a foliose lichen that attaches to rocks (cliffs, large boulders) by one central holdfast, hence the name Umbilicaria. Grey-brown, sometimes greenish, the lichen is disc-shaped. The upper side is hard with some wrinkles toward the central holdfast. White granules called "pruina" cover the surface. The lower side is covered in short black "hairs" called rhizines. The edges of the lichen are ragged and easily break off. The size of these lichens can be from a few centimeters wide up to the size of a saucer plate. This species reproduces through granules that cling to the rhizines and fall off onto the rock face, developing a new lichen structure. Spore-producing fruiting bodies (apothecia) are rarely seen on this species of Umbilicaria.
Umbilicaria americana is normally found on sheer granite rock faces such as cliffs and huge boulders. It prefers to grow in wet forested areas in sheltered sites. In really well suited sites, this lichen is abundant, covering entire rock faces. Look for it on the underside of smooth rock outcrops near a river or lake, or in wet forests