1. If the ubiquity hypothesis (i.e., "everything is everywhere) that has been proposed for microorganism is true, then particular species of myxomycetes should occur everywhere that suitable microhabitats exist. However, is this really the case?

2. Myxomycetes, ferns, mushrooms and bryophytes all reproduce by means of spores. Are dispersal potentials and distribution patterns comparable for all four groups or are they distinctly different for each group?

3. Some myxomycetes appear to be generalists and can be found in a variety of different microhabitats, whereas others seem to be restricted to specific microhabitats. Are these patterns consistent over a wide range of vegetation types and climates?

4. The myxomycetes of eastern North America, particularly the Northeast, are better known than is the case for any other region of the continent. However, based upon the collection records that are available, it would appear that some species are common in western North America but rarely encountered in eastern North America. Is this actually the case? If so, what factors of the over all environment are likely to be responsible?

5. There is little question that some species of myxomycetes are common while others are rare. Are changes in levels of abundance occurring (i.e., common species declining and certain rare species becoming more evident)? If so, can this be related to changes in climate or other landscape-scale factors? Do some species actually become locally extinct?

6. The vegetative stage of a myxomycete is in direct contact with the substrate upon or within which it occurs, and the pH of that substrate appears to represent a major ecological factor determining the distribution of particular species. For example, only certain species seem to be able to tolerate low pH conditions. Can these organisms be used as biological monitors to assess changes in the global environment on a regional or continental scale?

7. There is some evidence that the overall biodiversity of the assemblage of species of myxomycetes associated with a particular vegetation type is related to the biodiversity of the plants (particularly the woody plants) present, but this has never been evaluated on a regional or continental scale. To what extent does this linkage exist?

8. In temperate eastern North America, myxomycetes begin to appear in late May to early June and their fruiting bodies can be found until at least early October. Some species are likely to be found throughout this entire period, but most seem to have a definite phenology. However, there has never been an intensive study to determine to what extent this varies from year to year or from place to place (i.e., on a regional or continental scale). Would the body of data generated from such a study provide evidence of changes in the background environment?

The exact evolutionary affinities of the myxomycetes are still debated, but these organisms constitute a well-defined and homogenous group of approximately 875 species. Myxomycetes are characterized by a relatively complicated life cycle that was not understood completely until little more than a century ago. In brief, the life cycle consists of two very different trophic (or feeding) stages along with a reproductive stage that bears no resemblance whatsoever to either of the trophic stages. The first of the two trophic stages consists of uninucleate (single-nucleus) microscopic amoeboid cells that may or may not be flagellated. These amoeboid cells, derived from myxomycete spores that have germinated, feed and divide by binary fission to build up large populations in the microhabitats in which they occur. Myxomycetes spend this portion of their life cycle as true microorganisms, when their very presence in a given microhabitat can be exceedingly difficult, if not impossible, to determine. Ultimately, the amoeboid cells give rise to a second trophic stage, which consists of a distinctive multinucleate and often rather slimy-looking structure called a plasmodium. The transformation from one trophic stage to the other in the myxomycete life cycle is in most cases the result of fusion between compatible haploid amoeboid cells, which thus function as gametes. The fusion of the two cells produces a diploid zygote that feeds, grows, and undergoes repeated mitotic nuclear divisions to develop into the plasmodium. Plasmodia have no cell walls and exist as thin masses of protoplasm, which often appear to be streaming in a fanlike shape in the larger, more commonly encountered examples. Bacteria represent the primary food resource for both trophic stages, but plasmodia also are known to feed upon yeasts, algae, cyanobacteria and fungal spores. Most plasmodia are relatively small, but this is not always the case. In fact, some species are capable of producing plasmodia that are several meters across! Ultimately, a plasmodium gives rise to one or more fruiting bodies, within which the spores are produced.

The fruiting bodies of most myxomycetes are quite small, usually reaching no more than a millimeter or two in height, but some of them are objects of considerable beauty. Although large enough to be seen with the naked eye, fruiting bodies are best observed with a hand lens or microscope. Only then can their intricate nature be fully appreciated. Fruiting bodies may take the shape of tiny goblets, globes, plumes or other shapes more difficult to characterize. Some occur in tightly packed clusters, while others are scattered or even solitary. Many of the more intricate forms have a spore case held aloft on a delicate stalk, but others are attached to the substrate by their bases.

Most species of myxomycetes tend to be rather inconspicuous or sporadic in their occurrence and thus not always easy to detect in the field. Moreover, most fruiting bodies are relatively ephemeral and do not persist in nature for very long. Because of their life history strategy and inconspicuous nature, myxomycetes provide an immense challenge in biodiversity assessments and, consequently, often have been neglected in such studies. However, careful examination of suitable substrates (e.g., decaying logs and stumps) during summer and early fall, especially after a period of rainy weather, will invariably yield the fruiting bodies of a number of different species. It is not unusual to find half a dozen different species on a single log.

Although some myxomycetes appear to be generalists and can be found in many different ecological situations, others are almost invariably associated with particular types of substrates. For example, some species almost always occur on the decaying wood or bark of coarse woody debris, whereas others are more often found on dead leaves and other plant debris and only rarely occur on wood or bark. Interestingly, some species characteristically associated with decaying wood are restricted largely or completely to the wood from conifers, whereas others display a strong affinity for decaying wood from broadleaf trees. In addition to these substrates, myxomycetes also are known to occur on the bark surface of living trees, on the dung of herbivorous animals, in soil, and on aerial litter (i.e., dead but still attached leaves and other plant parts). The myxomycetes associated with decaying wood are the best known, because the species typically occurring on this substrate tend to be among those characteristically producing fruiting bodies of sufficient size to be detected easily in the field. Many of the more common and widely known myxomycetes, including various species of Arcyria, Lycogala, Stemonitis, and Trichia, are almost invariably associated with decaying wood. In contrast, most species of such genera as Diderma and Didymium are found almost exclusively on dead leaves and other types of non-woody plant debris. In a temperate forest, virtually all of the fruitings large enough to be readily observed in the field are associated on dead plant material (mostly forest floor litter and coarse woody debris) in contact with the ground. However, in a moist tropical forest, this is not the case, and many fruitings are found well above the ground on various types of aerial litter, including dead portions of vascular epiphytes and lianas.

Numerous images of myxomycetes, including most of the species one is likely to encounter in North America, are available in the searchable image database at http://slimemold.uark.edu and Discover Life.

The primary microhabitats for myxomycetes are decaying coarse woody debris (Picture 01), ground litter (dead plant parts on the ground), aerial litter (dead but still attached plant parts above the ground) and the bark surface of woody plants (Picture 02). Decaying portions of succulent plants, soil, and the dung of herbivorous animals represent three other microhabitats that support these organisms (Stephenson & Stempen 1994). In order to carry out a complete biodiversity inventory for the assemblage of myxomycetes associated with a particular locality, each of these microhabitats would be examined for the presence of myxomycete fruiting bodies that had developed under natural conditions in the field. When fruiting bodies (Picture 03) are observed, these would be collected or (for some of the more common species) recorded. A collection consists of all or (for extensive fruitings) some of the fruiting bodies along with a small portion of the substrate upon which they occur. Most people who study myxomycetes use a multi-compartment ("fishing tackle") plastic box (Picture 04) for temporary storage of collections in the field. Upon returning to the laboratory, it is important to open the box immediately. Otherwise, the moist conditions that exist within the unopened box will promote the growth of filamentous fungi that can quickly colonize the fruiting bodies of myxomycetes. Actually removing collections from the box and placing them on (for example) an old newspaper is recommended. Once the collections have air-dried, they can be placed in small pasteboard boxes for permanent storage. A complete description of the methods to be used is provided in Stephenson and Stempen (1994). The moist chamber culture technique (Picture 05) as it applies to myxomycetes represents an exceedingly useful method for supplementing the biodiversity data obtained from field collections. Moreover, the use of this technique will yield species that are rarely if ever encountered in the field (Picture 06). For some habitats (e.g., deserts) and microhabitats (e.g., the bark surface of woody plants), most of the species recorded are likely to be from moist chamber cultures. Sample material to be used in the preparation of moist chamber cultures should be collected from each of microhabitats (e.g., ground litter, aerial litter and bark) to be examined, placed in small paper (never plastic!) bags, and transported to the laboratory. If at all possible, sample material should be collected when it is dry. If this isn't possible, the samples should be spread out on old newspapers in the laboratory and allowed to dry out completely before being placed in culture. The usual procedure is collect enough material from a particular microhabitat to prepare three to five moist chamber cultures in the manner described by Stephenson and Stempen (1994). Although disposable plastic Petri dishes have been used in most studies, it is possible to use various other types of containers (e.g., small plastic boxes, butter dishes, zip-lock plastic bags, etc.) to prepare moist chamber cultures. Specimens of myxomycetes appearing in cultures should be removed and placed in small pasteboard boxes for permanent storage, in much the same manner as done for field collections. A complete set of information should be recorded with each myxomycete obtained in the field or from a moist chamber culture. This would include (a) the exact locality where it (or the sample material placed in moist chamber culture) was collected, (b) the type of habitat (e.g., broadleaf forest, pine forest, meadow, etc.), substrate or type of sample material with which it was associated, (c) the date the collection was made, and (d) the collector. The collecting site should be georeferenced (with a portable GPS receiver) whenever this is possible. If a digital camera is available, it is helpful to obtain a series of images to document the habitat and microhabitats being studied.

Decaying coarse woody debris Bark surface of woody plants Fruiting bodies Multi-compartment ("fishing tackle") plastic box Moist chamber culture technique

Species rarely encountered in field

Identification of myxomycetes is based almost entirely upon features of the fruiting bodies produced by these organisms. Fruiting bodies (also referred to as "sporophores" or "sporocarps" in some texts) occur in four generally distinguishable forms or types, although some species regularly produce what appears to be a combination of two types, apparently in response to certain (as yet undetermined) environmental factors. The most common type of fruiting body is the sporangium (Picture 03), which may be sessile or stalked, with wide variations in color and shape. The actual spore-containing part of the sporangium (as opposed to the entire structure, which also includes a stalk in those forms characterized by this feature) is referred to as a sporotheca. Other less common types of fruiting bodies are the aethalium, pseudoaethalium and plasmodiocarp.

It is possible to identify some of the more distinctive species of myxomycetes with a hand lens, but critical identification of many species requires the use of a stereomicroscope and/or a compound microscope. The most comprehensive taxonomic treatment of the species of myxomycetes that one is likely to encounter in North America is the monograph by Martin and Alexopoulos (1969), which has been out-of-print and thus difficult to obtain for a number of years. However, much of the information in the monograph (including images of all of the figures) is available on the web site http://slimemold.uark.edu maintained by the University of Arkansas. This same web site contains numerous images and other types of information relating to the myxomycetes. Lado (2001) provided the standard source of nomenclature currently used by most people who work with the group, but this information is also available through the web site mentioned above.

Alexopoulos CJ. 1963. The myxomycetes II. Botanical Review 29:1-78.

Blackwell M and RL Gilbertson. 1980. Sonoran desert myxomycetes. Mycotaxon 11:139-149.

Farr ML. 1976. Myxomycetes. Flora Neotropica, Monograph No. 16. The New York Botanical Garden, New York.

Lado C. 2001. Nomenmyx. A Nomenclatural Taxabase of Myxomycetes. Cuadernos de Trabajo Flora Micológica Ibérica 16:1-221.

Martin GW and CJ Alexopoulos. 1969. The Myxomycetes. University of Iowa Press, Iowa City.

Martin GW, CJ Alexopoulos and ML Farr. 1983. The Genera of Myxomycetes. University of Iowa Press, Iowa City.

Novozhilov YK, M Schnittler, AW Rollins and SL Stephenson. 2000. Myxomycetes from different forest types in Puerto Rico. Mycotaxon 77:285-299.

Schnittler M. 2001. Ecology of myxomycetes from a winter-cold desert in western Kazakhstan. Mycologia 93:653-669.

Schnittler M, C Lado and SL Stephenson. 2002. Rapid biodiversity assessment of a tropical myxomycete assemblage-Maquipucuna Cloud Forest Reserve, Ecuador. Fungal Diversity 9:135-167.

Schnittler M and SL Stephenson. 2000. Myxomycete biodiversity in four different forest types in Costa Rica. Mycologia 92:626-637.

Stephenson SL and GA Laursen. 1993. A preliminary report on the distribution and ecology of myxomycetes in Alaskan tundra. Bibliotheca Mycologica 150:251-257.

Stephenson SL and GA Laursen. 1998. Myxomycetes from Alaska. Nova Hedwigia 66:425-434.

Stephenson SL and H Stempen. 1994. Myxomycetes: a Handbook of Slime Molds. Timber Press, Portland, Oregon.

Stephenson SL, I Kalyanasundaram and TN Lakhanpal. 1993. A comparative biogeographical study of myxomycetes in the mid-Appalachians of eastern North America and two regions of India. Journal of Biogeography 20:645-657.

Stephenson SL, Y Novozhilov and M Schnittler. 2000. Distribution and ecology of myxomycetes in high-latitude regions of the northern hemisphere. Journal of Biogeography 27:741-754.

Stephenson SL, M Schnittler and C Lado. 2004a. Ecological characterization of a tropical myxomycete assemblage-Maquipucuna Cloud Forest Reserve, Ecuador. Mycologia 96:488-497.

Stephenson SL, M Schnittler, C Lado, A Estrada-Torres, D Wrigley de Basanta, JC Landolt, YK Novozhilov, J Clark, DL Moore and FW Spiegel. 2004b. Studies of Neotropical mycetozoans. Systematics and Geography of Plants 74:87-108.