Caloplaca: Fire Dot Lichen

Tuesday, June 30, 2009

Nature Notes
by Bob Thomas

Arguably, the most abundant lichen in the New Orleans area goes completely unnoticed by all but the most observant naturalist. Even the best naturalists, who may notice them, have no idea what they are.

The crustose lichen in question grows on calcareous substrates and appears as a rusty crust on sidewalks and streets. On very close examination, it is composed of very tiny apothecia (you will need good magnification to see these), disk-shaped fruiting bodies (ascomata, or ascoma) that produce and house ascospores (the actual sexual spores of the lichen). The thallus (the vegetative body of the lichen) is not evident.

Due to the small apothecia, and the fact that many of the species are bright orange, red, or yellow, this group of lichens is often called fire dot, or jewel lichens.

Our "sidewalk" fire dot lichens are a species of the geographically wide-spread genus Caloplaca, which has only a few species in the southern United States.

The U.S. expert on this group is Dr. Clifford Wetmore (University of Minnesota). By examining only photos, he suggests our species is either Caloplaca holocarpa or C. crenulatella, with the latter more typical of calcareous rocks. The jury will still be out on the exact species identification until he or other lichenologists have specimens in their labs. Dr. Bob Egan (University of Nebraska Omaha) says that one must examine the spores and other microscopic characters of the apothecium in order to know the species.

Special thanks in this quest of identification are due to Drs. Russ Chapman and Shirley Tucker (both of the University of California San Diego, and both formerly at Louisiana State University).


Caloplaca on the sidewalk in Metairie, La.                                Caloplaca on concrete in Paul B. Johnson
Photo by Bob Thomas.                                                         State Park, Miss.
                                                                                              Photo by Shannon Fortenberry.

Caloplaca on concrete in Paul B. Johnson
State Park, Miss.
Photo by Shannon Fortenberry.