Home


Macrofungi


by
Gregory M. Mueller
The Field Museum, Chicago
Macrofungi are a diverse, commonly encountered, and ecologically important group of organisms. Like most fungi, the major part of these organisms consists of a mass of thin, microscopic threads (termed mycelium) growing in soil, decomposing leaves, and other substrate. They differ from other fungi by forming large, macroscopic fruitbodies at some time in their life; the mushrooms sold in grocery stores are an example of these fruitbodies. This group of fungi includes all mushrooms (Fig. 1), morels, puffballs, bracket fungi, and cup fungi.
Macrofungi are vitally significant in forests; many species help break down dead organic material, such as dead tree trunks and leaves, into simple compounds usable by growing plants. Thus, they act as nature's recyclers, without which forests could not function. Some species are major plant pathogens (causes of disease) that cause millions of dollars of damage to U.S. forests each year. Still other species enter into a necessary, mutually beneficial association with trees such as oaks, pines, firs, and spruces. In this association (Fig. 2), termed mycorrhizae, the mycelium of the fungus brings water and nutrients to the tree in return for taking excess food from the tree. Neither the tree nor the fungus can survive without the other. Finally, some of these fungi form an important part of the diet of many small mammals and insects. For example, small truffle-like fungi are a major food source of the northern flying squirrel (Glaucomys sabrinus; see box). Because macrofungi are an indispensable component of the forest ecosystem, information on which fungi occur in the forests and on the specific role that they play is necessary for management and maintenance of our forests.

Fig. 1. Entoloma salmoneum. The salmon-colored entoloma is a common recycler of forest litter in North American forests. Courtesy G.M. Mueller, The Field Museum
Fig. 2. Mycorrhizae formed between ponderosa pine and Laccaria laccata in the laboratory. Note the branched pine roots and threadlike fungal hyphae. Courtesy G.M. Mueller, The Field Museum
Macrofungi also directly affect people. Though some fungi are deadly poisonous, others are prized as edibles. Commercial mushroom harvesting is a multimillion-dollar-a-year business in the United States; for example, the industry added an estimated $40 million to the Oregon economy in 1993 alone. Additionally, several thousand amateur mushroom hunters in the United States collect solely for their own enjoyment.

Number of Species
Considering the human, ecological, and economic importance of these organisms, it is somewhat surprising that there is not a good estimate of the number of species of macrofungi that occur in North America. Because there are neither checklists of North American mushrooms and their relatives nor comprehensive regional treatments, the best estimates of North American diversity are based on comparisons with numbers of these organisms reported from Europe. More than 3,000 species of mushrooms and their relatives are reported from western Europe (Moser 1983), but most scientists who study fungi (mycologists) would estimate that far more species occur in North America. For example, more than twice as many species of Lactarius, Amanita, and Clitocybe are reported from the continental United States (Hesler and Smith 1979; Bigelow 1982, 1985; Jenkins 1986) than from western Europe (Moser 1983).
Better estimates exist for species diversity of the other groups of North American macrofungi. Gilbertson and Ryvarden (1986, 1987) treated more than 400 species of polypore fungi, Smith et al. (1981) listed nearly 300 species of puffballs and relatives, and Seaver (1942, 1951) covered more than 350 species of cup fungi and other macro ascomycetes. Based on these data, it is reasonable to predict that there are 5,000-10,000 species of macrofungi in the United States. A compilation of herbarium records in U.S. and Canadian museums and universities would provide a good first step in predicting the diversity of these organisms.

Declining Fungi
Fig. 3. Cantharellus cibarius. The chanterelle is one of the important fungi forming mycorrhizae with pines and oaks in North American forests. Courtesy G.M. Mueller, The Field Museum
Change in the frequency of occurrence of macrofungi in Europe is well documented; many species that form ectomycorrhizae (a kind of mycorrhizae; see glossary) are showing a marked decline, and some species involved with wood decay show a marked increase in fruiting. More than 50% of the reported species of mushrooms in Europe occur on at least one country's "Red List" (see glossary: "red data book") (Arnolds and de Vries 1993), and once-common species such as Hydnum repandum and some of the chanterelles (Fig. 3) appear lost from some countries. Air pollution, particularly acid rain, has been implicated in this observed decline in ectomycorrhizal fungi fruiting frequency and diversity in Europe (Fellner 1993; Pegler et al. 1993). Intensive collecting of edible fungi such as chanterelles, Hydnum, and boletes might also be negatively affecting fruiting patterns of these fungi, but additional data are needed to document this. In any case, the observed change in fungal fruiting is correlated with a decline in forest health, but cause and effect are hard to document. Rigorous studies to determine if similar trends in macrofungi fruiting patterns have occurred in the United States do not exist.

Current Studies of Diversity
The baseline data necessary for estimating fungal diversity and for investigating trends in fruiting patterns and frequencies of macrofungi in the United States and Canada are not yet available although various methods are beginning to be used to obtain these necessary data. For example, studies of species diversity and frequency of particular fungi in Pacific Northwest old-growth forests have documented that while a single season of collecting will uncover most of the decomposer macrofungi, mycorrhizal fungi fruit much more erratically (Vogt et al. 1992). Thus, to develop a reasonable estimate of species richness and dominance, researchers must sample over several years. These studies also have documented that certain collecting techniques work better for some fungi than others, which emphasizes the need to develop standardized sampling protocols for collecting data on fungal species' richness and fruiting patterns.
Satellite imagery has been combined with a long-term mapping program of fungal fruitbodies to assess the relative health and growth of particular tree-mycorrhiza fungus pairs in southern Mississippi (Cibula and Ovrebo 1988). This approach shows great promise for directly investigating the effect of certain fungi on tree health. These data, however, are based only on aboveground information, and there is still some question about how well the appearance of fruitbodies growing under a particular tree predicts what fungi are forming mycorrhizae with that tree at that time. To address this question, researchers have developed molecular techniques using DNA amplification procedures to compare the mycorrhizae on the roots of certain trees with fungal fruitbodies occurring near the tree (Bruns and Gardes 1993). The preliminary data documented that there is not always a one-to-one correlation between fruitbodies and mycorrhizae, and that caution must be used when using fruitbodies alone.

Further Studies
The studies mentioned in this article illustrate the range of work in the United States on assessing diversity and determining possible changes in fruiting patterns of macrofungi. More work is needed to document the status and trends of macrofungi in North America. These data are vital because of the integral role that macrofungi play in forest systems as decomposers and recyclers, plant pathogens, mutualists, and food for small mammals, and because of the growing commercial importance of these fungi.
For further information:
Gregory M. Mueller
The Field Museum
Department of Botany
Chicago, IL 60605
References
Arnolds, E., and B. de Vries. 1993. Conservation of fungi in Europe. Pages 211-234 in D.N. Pegler, L. Boddy, B. Ing, and P.M. Kirk, eds. Fungi of Europe: investigation, recording and conservation. The Royal Botanic Gardens, Kew, U.K.

Bigelow, H.E. 1982. North American species of Clitocybe. Part 1. Beihefte zur Nova Hedwigia 72:5-280.

Bigelow, H.E. 1985. North American species of Clitocybe. Part 2. Beihefte zur Nova Hedwigia 81:281-471.

Bruns, T., and M. Gardes. 1993. Molecular tools for the identification of ectomycorrhizal fungi: taxon-specific oligonucleotide probes for suilloid fungi. Molecular Ecology 2:233-242.

Cibula, W.G., and C.L. Ovrebo. 1988. Mycosociological studies of mycorrhizal fungi in two loblolly pine plots in Mississippi and some relationships with remote sensing. Pages 268-307 in J.D. Greer, ed. Remote sensing for resource inventory, planning and monitoring. Proceedings of the Second Forest Service Remote Sensing Application Conference. American Society for Photogrammetry and Remote Sensing, Falls Church, VA.

Fellner, R. 1993. Air pollution and mycorrhizal fungi in central Europe. Pages 239-250 in D.N. Pegler, L. Boddy, B. Ing, and P.M. Kirk, eds. Fungi of Europe: investigation, recording and conservation. The Royal Botanic Gardens, Kew, U.K.

Gilbertson, R.L., and L. Ryvarden. 1986. North American Polypores. Vol. 1. Fungiflora A/S, Oslo. 433 pp.

Gilbertson, R.L., and L. Ryvarden. 1987. Pages 437-885 in North American Polypores. Vol. 2. Fungiflora A/S, Oslo.

 Hesler, L.R., and A.H. Smith. 1979. North American species of Lactarius. The University of Michigan Press, Ann Arbor. 841 pp.

Jenkins, D.T. 1986. Amanita of North America. Mad River Press, Eureka, CA. 198 pp.

Moser, M. 1983. Keys to the Agarics and Boleti (Polyporales, Boletales, Agaricales, Russulales). Roger Phillips, London. 535 pp.

Pegler, D.N., L. Boddy, B. Ing, and P.M. Kirk, eds. 1993. Fungi of Europe: investigation, recording and conservation. The Royal Botanic Gardens, Kew, U.K. 322 pp.

Seaver, F.J. 1942. The North American cup fungi (Operculates). Rev. ed. Seaver, New York. Reprinted by Lubrecht and Cramer. 377 pp. + 74 plates.

Seaver, F.J. 1951. The North American cup fungi (Inoperculates). Seaver, New York. 428 pp.

Smith, A.H., H.V. Smith, and N.S. Weber. 1981. How to know the non-gilled fleshy fungi. 2nd ed. William C. Brown, Dubuque, IA. 324 pp.

Vogt, K.A., J. Bloomfield, J.F. Ammirati, and S.R. Ammirati. 1992. Sporocarp production by Basidiomycetes, with emphasis on forest ecosystems. Pages 563-581 in G.C. Carroll and D.T. Wicklow, eds. The fungal community. Marcel Dekker, Inc., New York.


Home