Discussion of Winter fungi

During an afternoon tea break back in the early 1970's Ruth Horner Arnold, a Canadian authority on pyrenomycetes, remarked that she regularly did her fungus collecting in winter. Ruth lived in the Gatineau Hills, across the river from Ottawa, an area with snowy winters and very hard frosts; hardly a place that most mycologists would associate with productive January collecting. Of course she was right, many fungi can be found under these conditions and most of these fungi are alive and well. Bring them indoors, thaw them out and they will begin to discharge their spores with great vigour. A look at the winter checklists reveals that a great diversity of Ascomycota and Basidiomycota can be found in winter. Even if the abundance of species is lower in winter than in summer the taxonomic diversity is nearly as great.

Effects of winter on fungi

Winter survival is an important factor in the lives of cold-climate organisms. Freezing temperatures cause ice crystals to form within and around living cells. Intracellular (within the cell) freezing results in mechanical damage to sensitive cell membranes by the formation of ice crystals. Extracellular (outside or around the cells) freezing is more complex according to Snyder and Paulo de Melo-Abreu (Frost Protection: fundamentals, practice and economics, FAO, Rome, 2005). Although the damage here can also be mechanical it may often be the result of severe dehydration. Ice crystals forming around the outside of the cell cause water inside the cell to pass out through semipermiable cell membrances and become deposited on the ice crystals, causing the cell to become extremely desiccated. Because of this dehydration, fungi found in very cold climates may resemble those found in warm but very dry climates. Frost hardiness has not been extensively studied in fungi, but if it involves mechanisms similar to those known for desiccation-tolerance it may be brought about by the presence of polyols (glycerol, mannitol and other related compounds) in the cytoplasm of the cells. Snyder and Paulo de Melo-Abreu also discuss the rate of cooling on plant survival. Rapid cooling often results in higher mortality of plant tissues than more slow cooling, especially when intracellular ice crystals are involved, although they point out that rapid cooling may be less frequent in nature than in the laboratory. The whole issue of desiccation becomes important to the winter mycologist because most of the fungi he or she will find are those attached to exposed plant surfaces such as the trunks of trees, branches above snowline and dead but still attached conifer needles. These fungi are must not only tolerate the cold but must survive exposure to the extremely dry winter air.

Winter and the life histories of fungi

Fungi can be classified according to their mode of nutrition into biotrophs, nectrotrophs and saprotrophs. Biotrophs are those that obtain their nutrition from living cells of another organism. They are said to be parasitic if they live at the expense of the other organism, or mutualistic if they give the other organism something beneficial in return. Necrotrophs also require living organisms for their nutrition but unlike biotrophs they kill the tissues they require before they consume them. Saprotrophs consume only dead materials. Of course there are intermediates between these types and some that may take up one mode of nutrition during part of their lives and switch to another at another stage. Although biotrophs and necrotrophs abound in all biological communities they tend to be less conspicuous in winter. The reason for their apparent rarity in winter is that they usually have life histories ivolving the recolonization of a host when it begins its spring and summer activities. Species such as Cordyceps variabilis, Melampsorella caryophyllacearum or Mycophycias ascophylli do not appear until winter is long gone, because their insect, plant or algal hosts are not receptive until then. This is why May and June are particulary good months for collecting biotrophs and nectrotrophs.

Winter is a good season for saprotrophs. Their sources of nutrition are the dead plant, fungal and animal materials exposed to the environment ready to be consumed. The first fungi to become established on them may be the ones that get the most benefits. The fungus that waits until May or June to colonize a branch killed by winter storms may be too late because all the avilable colonization sites have already been occupied by earlier arrivals. The successful species are often those that can release spores as soon as above-freezing temperatures arrive. These species have fully mature fruiting structures in the middle of winter and are the ones we seek when we put on snowshoes and go out for a walk.

Where to look

In most parts of Canada there will be a cover of snow during January and February, and fungi can be found both above and below it. Snow is an excellent insulator both against tempeature extremes and desiccation. On the other hand the snow cover will prevent most fungi from casting their spores to the wind early in the season, and thus final maturation of fruiting structures may occur only gradually during early spring. March and April is a good time to search out the parasites of emerging spring annuals. Although some larger branches and logs lying under the snow may support good growths of certain Basidiomycota this is not a prime location of mid-winter collecting. Instead, search the branches, twigs, trunks and attached needles above the snow. Here you will find the greatest diversity of early-rising fungi. Branches with bark still attached often harbour interesting fungi below loosened portions of bark. Totally decorticated (barkless) branches are micro deserts requiring years of slow decay before they disappear. These habitats are home to many long-lived fruiting structures. The picture at right illustrates three pieces of green alder wood (Alnus viridis) collected in late November. The leftmost piece is partially decorticated, perhaps as recently as when it was collected. The middle piece still has all its bark and is heavily colonized by Fuscoporia ferrea. The right-hand piece is totally decorticated and dry. All of the samples have been colonized by lichenized- as well as non-lichenized fungi. The large basidioma of F. ferrea was mature and functional, producing a white spore print.

Two checklists are presented here, one for Ascomycota and one for Basidiomycota. Both lists had their beginning in an annual mycology course given at the University of Toronto in the years 2000 to 2003. Part of this course involved a week-long February field trip to Algonquin Provincial Park in Ontario where students went out each day on snowshoes searching for fungi. At the end of the course in April students were required to submit a collection of identified fungi representing both Ascomycota and Basidiomycota. For most students the February field trip was their main source of specimens. The result of this course was the accumulation of a list of identified fungi found in February in a fairly cold region of Ontario. Since 2003 the project has moved to New Brunswick, also a region with good cold winters and kinds of fungi similar to those found in Ontario.

The checklist of winter fungi has been divided into two for convenience; it's simply easier to browse a short list than a long one. In addition, most collectors seem to prefer one group over the other. As with all lists on this site each record must be backed by a dried herbarium specimen in a recognized institution. Those marked "ONT" were collected in Ontario, mostly Algonquin Provincial Park, and are represented by one or more specimens in the Fungarium of the Royal Ontario Museum in Toronto (TRTC). Those marked "NB" are from New Brunswick and are represented by specimens in the herbarium of the New Brunswick Museum in Saint John (NBM). All of the fungi on the lists were collected during January and February. Although late December and early March are nearly as cold as January and February it was decided that these months of seasonal transition would be excluded.

Some identifiable fungi may be found in the winter even though they are no longer functional. A truly functional ascoma or basidioma should be able to discharge its spores when warmed to above freezing and placed in a moist environment. Some, the birch polypore (Piptoporus betulinus) for example, can often be found on dead birch trunks during the winter yet will be incapable of releasing basidiospores. These structures are no longer functional and are present only because they are not yet decayed. Technically these fungi should not be on a winter list but have been retained because they were collected by a number of students and are conspicous even when they are senescent.

Many fungi will be inconspicuous when first brought indoors. Some will be discovered in the field and even tentatively identified, but later examination of the substrate will often lead to the discovery of other inhabitants. Since winter fungi are able to withstand long periods of dryness, collections need not be examined immediately after they are brought in. Just store them in a dry place until you are ready to look at them. When you are ready to work on them take substrate materials of a convenient size and soak them in water for an hour or so. Following this soaking a variety of very inconspicuous fungi will become visible, especially if you examine them with a dissecting microscope. If they are "true" winter fungi they should be able to produce and discharge spores. The easiet way to test this is to suspend a moistened specimen over a microscope slide, either by placing it directly on the slide or resting it on two matchsticks and leave it in a covered container overnight. The container should have a moistened piece of paper towel in it to keep the humidity close to 100%. By morning most fungi will have left a visible spore print on the slide. Some fungi need a little more time to get their systems up and running and will not discharge spores immediately after being moistened. If you fail to obtain a spore print in the first few hours leave the specimen in place and give it another 24 hours.

The lists presented here are not even close to complete. At this stage in their development they represent only a small sample of the species to be found in winter. However they do offer a challenge to collectors and a reminder to Canadian mycologists that winter is an excellent time to get into the field.