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Nature Notes
by Bob Thomas

One of the most beautiful fungal species is cobalt crust, which is also known as “velvet blue spread,” or simply “blue velvet on a stick.” Although its correct scientific name is Terana caerulea, it is most often referred to as Pulcherricium caeruleum. Those pesky rules of nomenclature exist to ensure an orderly system of taxonomy based on rules of priority, but their adherence occasionally creates change, thus causing confusion for the non-specialist.

For those of us who love the color blue, this is our special fungus. Cobalt crust is a splendid exhibition of what the word cobalt really means. The specimen photographed in Hattiesburg, Ms., however, is lavender, not blue. I have found nothing to help me understand this difference, and it may be related to drying and inactivity, a misidentification, or something new to science!

A word about where this species stands in the taxonomic world of the Kingdom Fungi (some taxonomic levels are skipped to spare you of too many new words, but give you their position within the kingdom): they belong to the Subkingdom Dikarya (the higher fungi, what most people think of when someone says “fungi”), Phylum Basidiomycota (mushrooms, bracket fungi, puffballs, etc.), Order Polyporales (bracket fungi and cobalt crust and relatives), and the Family Phanerochaetaceae (its specific family).

Cobalt crust is a member of a grouping of fungi called corticioid fungi, members of which are also called crust fungi (meaning they adhere to the surface of their substrate) or resupinate fungi (meaning their fruiting body is against the surface of the substrate, not on a stalk). Corticioid fungi are not a group related by common ancestry (in other words, not a monophyletic group), but a group defined by having a set of shared common characteristics. For biologists, they are like the group “mangroves:” woody vegetation species that are not closely related, but have in common that they all grow in and around salt water and possess characteristics that allow them to exploit that habitat.

Cobalt crust often grows as a sprawling crusty fungus, very often under logs, rendering them invisible to the average person who walks through the woods. Flip a few logs and one is rewarded with a variety of species of crusty growths of white, red, orange, tan, blue, and more. BTW, after taking a look under the log, turn it back to its original position to preserve the microhabitat that has taken some time to develop. Be gentle!

When moist, cobalt crust is soft to the touch; when dry, it is crusty and brittle.

Cobalt crust is a white rot fungus, meaning it is a very effective agent of decay for plants in that it can break down all components of the plant cell wall, including sturdy brown lignins, thus leaving the white cellulose exposed. It is a saprobic crust fungus, meaning that it efficiently breaks down plant materials to their base components (starches to simple sugars, proteins to amino acids, and lipids to fatty acids and glycerol). One could speculate that if it were not for the crust fungi breaking down fallen limbs and logs, we would be well over our noses in logs and other woody materials!

This species can be used to produce an antibiotic named cortalcerone that inhibits the growth of Streptococcus pyogenes, a spherical bacterium that is responsible for an abundance of infections.

Cobalt crust is distributed worldwide in warm to temperate environs, and is known from the southeastern U.S., and diverse geographic areas including but not limited to Turkey, the Canary Islands, Africa, Europe, and much of Asia.

Crust fungi, in general, are very common. They prefer humid deciduous forests, usually on undersides of logs or lower sides of branches so fruiting bodies easily drop their pale blue or glass-like (hyaline) spores. However, it is not uncommon to find them growing on dead hardwood limbs on the ground, completely covering the branch.

Since they do not use the air to distribute zillions of spores as do mushrooms, crust fungi compensate by producing their spores from early spring to late fall. They are very hardy and can dry out and then become active when they rehydrate, allowing them to live through a variety of conditions and seasonal changes.

The lavender coloration of the Hattiesburg specimen is still bothersome. I’ve seen photos of a similar growth form named violet crust, Chondrostereum purpureum. Crust fungus expert Dr. David Hibbett of Clark University believes that identification is possible for my specimen, but that the absence of a pileus (mushroom cap) or reflexed margins (where the edges bend back to form a pileus) suggest it is Terana caerulea.

Unfortunately, I no longer have the specimen – only the photo. Therefore, the final jury is still out! Fun.


“Fruiting bodies are a thin layer of hyphae (called a subiculum) on the surface of the log with a layer of basidia to the outside. These basidia, which always point downward, form and disperse the spores. “

(Science: microbiology) The fine, branching tubes which make up the body (or mycelium) of a multicellular fungus.

See hymenium, which is exposed on the outside

Ginns, J. and M. N. Lefebvre. 1993. Lignicolous corticioid fungi (Basidiomycetges) of North America. Mycological Memoir 19, APS press, 247 pages.


Cobalt crust, Terana caerulea, is a velvety crust                                Another image of the same specimen.                    
fungus. This specimen from Hattiesburg, Ms.,                                    Photo by Bob Thomas. 
is lavendar as opposed to the norm of blue.
This specimen was photographed in April on a
stick in a wood pile in the city.
Photo by Bob Thomas.


In this photo, it is obvious why the fungus is                               A typical growth pattern for Cobalt crust. It
also called velvet blue spread.                                                    usually grows on the bottoms of limbs or under
This photo was taken in Germany.                                               logs to facilitate dropping its spores by gravity.
Photo by                                                             Photos are usually taken with the limb/log
                                                                                                turned over, for obvious reasons.
                                                                                                   Photo by Wikipedia.