Challenges posed by fungal morphology and life cycles
The morphology and life cycles of fungi pose special challenges for biologists, but also provide some research opportunities that are not available in other organisms.
Finding fungi in nature .
Many fungi are microscopic, making it very difficult to detect them in nature. One way to detect fungi is to culture them out of natural substrates, but some fungi cannot be cultured and will evade such methods. Fungi that produce multicellular fruiting bodies are hard to detect when they are not actively fruiting. It is difficult to estimate the number of fungal species that occur in any given habitat, which is one reason for the gap between the numbers of known fungal species (70,000) and the estimated total number of fungal species (1.5 million).
Determining the boundaries of an individual fungus.
Because of the mycelial form of fungi it is difficult to assess the spatial extent of individuals. If two mushrooms of the same species are growing out of a log, how do we know if they are produced by the same mycelium? One way to tell is to culture the mycelium from both mushrooms and confront them in vitro. If they are from the same individual, the mycelia should fuse. If they are from different individuals, they should have an antagonistic interaction. This is time consuming and is not an option for the many fungi that cannot be cultured. Because it is so difficult to delimit individuals, we actually know very little about the longevity, mating relationships, and behavior of most fungal species.
Microscopic fungi provide few morphological characters for discriminating species (e.g., yeasts). Even mushrooms are anatomically simple and they often have subtle, continuous variation. Consequently, many named species of fungi actually contain multiple cryptic species. The 70,000 known species of fungi probably contain many more cryptic species.
Connecting the sexual and asexual forms of fungi.
Fungi are rarely encountered in nature with both the sexual and asexual phases present. Consequently, parallel taxonomies have been developed for asexual and sexual forms. The Deuteromycetes is an artificial (non-monophyletic) grouping of asexual fungi. One way to make anamorph-teleomorph connections is to grow the fungi in culture in the hope of getting them to express both phases of the life cycle. This is tricky. A major focus in fungal systematics is the establishment of anamorph-teleomorph connections and integration of the parallel classification systems.