Sarea difformis: A fungus that lives on conifer resin

**Black spruce resin with *Sarea difformis*.**

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.

**A few small fruiting disks (marked by red arrows) of the fungus *Sarea difformis* are growing on the darker portions (are those part of the fungal body?) of the resin. Can you find more?**

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

Sunrise

A Few More Spring Flowers

Red maple flowers (Acer rubrum)

Staminate catkins of quaking aspen (Populus tremuloides) floating in a pond.

Tea-leaf willow pistillate flowers (Salix planifolia)

Prairie willow staminate flowers (Salix humilis)

More flowers on shrubs and trees from around here. Trees like red maple (Acer rubrum) and quaking aspen (Populus tremuloides) and shrubs such as tag alder (Alnus incana), hazel (Corylus spp.), and willow (Salix spp.) are the first flowers of spring appearing before the more familiar spring ephemeral wildflowers that grow in forests.

Soon there will be other flowers in bloom. Hepatica (Anemone americana), stalked sedge (Carex pedunculata), and wood rush (Luzula acuminata) will come into flower in the next few days. These low growing plants occupy spaces on the forest floor and today on one of my rambles I noticed that many already have unopened flower buds.

An Afternoon in the Woods

Hardwood swamp still frozen but not for long.

On Saturday I took a canoe trip down the little stream with the big name (West Fork of the Moose Horn River) that passes through my property to visit the western section. This area is approximately 56 acres and forested. Most of it is upland aspen and spruce forest but there is a large hardwood swamp near the southern property line.

Another part of the swamp (finally) thawing out. Soon this will be a flowing stream.

The ground was still snow covered but it was melting fast in the warm sun. I spent most of my time in a portion of a hardwood swamp looking at tree trunks for lichens and fungi. I found several lichen species previously documented from here and possibly one new species for the list. There are also a number of unknown lichen specimens to figure out.

Shadow Lichen (Phaeophyscia orbicularis?) on a sapling black ash tree.

Shadow Lichen (Phaeophyscia sp.) with an unknown gray foliose species on a small but old red maple.

Shadow Lichen (Phaeophyscia sp.) on a sapling black ash tree.

Lung Lichen (Lobaria pulmonaria) on a small but old red maple

Appalachian Punctelia (Punctelia appalachensis) on a black ash tree.

Powdered Fringe Lichen (Heterodermia speciosa) on a black ash tree.

Frost Lichen (Physconia sp.) on a black ash tree

Saucer Lichen (Ochrolechia trochophora) on a black ash tree.

Four lichens: Script Lichen (Graphis scripta in upper right) and three unknowns.

There were two fungi that interested me. One is Phellinus igniarius, a polypore bracket fungus, that was growing on the trunk of an old quaking aspen. This fungus decays the lignin in the wood leaving behind the lighter colored cellulose and is one of the causes of white-rot in hardwood trees. The other fungus looks like P. igniarius and like it causes decay in living hardwoods. This one seems to only grow on black ash trees. It is a polypore but the pore surface looks shaggy rather than smooth. So far no luck in figuring it out.

Phellinus igniarius on quaking aspen.

Unknown bracket fungus on black ash.

Most of the trees in the hardwood swamp are black ash (Fraxinus nigra) with some green ash (F. pensylvanica), yellow birch (Betula allegheniensis), paper birch (B. papyrifera), American elm (Ulmus americana), quaking aspen (Populus tremuloides), and red maple (Acer rubrum). A year ago I measured the trees in the lower two-thirds of the swamp to get a population count by species and to calculate basal area. Some of the black ash trees are huge (for this part of Minnesota anyway). Of the 64 black ash measured 14 were between 28 cm and 44 cm in diameter. There were also 12 yellow birch in this size range. Black ash and yellow birch are slow growing trees even on good sites like this one so it is possible that the largest trees are at the century mark.