Conifer resin oozing from a tree is an inhospitable place. The terpenoid chemicals in resin are toxic to many forms of life, but not all. Even though conifer resins are full of anti-fungal and anti-bacterial compounds, some organisms have found a way around that. One of these is a fungus called Sarea, a genus of fungi that grows on the resins of pines, spruces, firs, and cedars. Organisms that live on resins are called resinicolous (resin plus “colous” meaning “inhabitant”).
From lichen to fungus
At one time, Sarea was thought to be a lichen, but because it lacks a photobiont (symbiotic photosynthetic organism), it has been “demoted” to a fungus. The tiny (barely 1 mm across) fungus bodies pictured above and below growing on the resin of a black spruce are, to the best of my knowledge, the apothecia (reproductive structures) of Sarea difformis. Cross-sections of the fruiting body examined under a microscope would make identification more certain, but that’s a bit out of my reach right now.
I have looked for research papers on how Sarea can live on conifer resin, but the results have not yielded much information. Does it actually break down the resin components into simple carbohydrates? If so, then does it do this on its own, or is there a symbiotic relationship with bacteria or another fungus? Are the fungal hyphae growing in the resin or merely on top? How does it disperse? A lot of questions, and I’m sure there are answers somewhere.
Taxonomy
Sarea is a genus in the phylum Ascomycota (cup fungi, sac fungi), which includes familiar mushrooms like morels and the blue mold in Roquefort cheese. The taxonomy of the genus Sarea is not entirely settled, so some species may be moved to other genera, and species from other genera may be moved to Sarea. Also, new species are being discovered.
A similar resinicolous species that might be encountered in northern coniferous forests is Sarea (Zythia) resinae. It can be distinguished morphologically by the color of its apothecia. Sarea difformis has black apothecia, and Sarea resinae has orange apothecia.
Rare?
Sarea is not a rare fungus, but because of its small size and peculiar habitat, it is just rarely seen. It occurs throughout the cooler regions of the northern hemisphere.
Sources and additional reading
- Consortium of Lichen Herbaria: Sarea
- The British Lichen Society: What is a Lichen?
- Sarea cirrhendocarpa, a fungus species new to science from the southern Rocky Mountains
- Encyclopedia Britannica: Ascomycota
- Composition analysis of exudates produced by conifers grown in Taiwan and their antifungal activity
- Conifers protect themselves against bark beetles with substances from two eras
Not Very Far Away 
Interesting. We don’t have a lot of black spruce here but I wonder if this fungus lives on other conifers.
Also interesting is how the fruiting disks look very similar to those I find on toadskin lichen (Lasallia papulosa.)
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I would think so especially on red spruce but probably any conifer with abundant resin flow. The ones I found were on a resin flow where a I’d sawed off a small branch several years earlier. I saw some similar black fruiting disks on a conch (Phellinus) growing from an aspen tree but I don’t know what they were..
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