Aquatic hyphomycetes

Tetracladium marchalianum conidia on conidiophores sticking out of a substrate.

Aquatic hyphomycetes (also known as Ingoldian or freshwater fungi) are anamorphic (asexual) fungi that live in aquatic habitats. This group of fungi is mostly classified based on their morphology. Most aquatic hyphomycetes are ascomycetes, but members from other groups are found as well, such as mitosporic basidiomycetes. Aquatic hyphomycetes belong to an asexual stage of a fungus life cycle, and most of these species have not had their teleomorph (sexual) stage identified, if one exists.

Ecology

Aquatic hyphomycetes live in aquatic habitats, most often in well-aereated freshwater streams on leaf litter and other decaying plant material, but are also found in marine environments, estuarine environments, ponds, and lakes. They are primarily saprotrophs, and break down leaves, or wood, together with bacteria, and other organisms such as oomycetes. This decomposition makes nutrients available for other organisms that can't break down or use these nutrients on their own. They therefore facilitate for other organisms—for example groups like benthic insects eating leaves conditioned by fungi and bacteria. Some species have also been observed as being endophytes in the roots of riparian plant species, and other species are observed to be mycoparasites. Aquatic hyphomycetes play a bigger role in nutrient cycles when making difficult-to-break-down molecules, like cellulose, and other nutrients like nitrogen more available for other organisms, such as insects and fish.

Aquatic hyphomycetes are also considered important bioindicators of ecosystem health, because many of these species are sensitive to stress factors in the environment, like pollutants or temperature. However, many of these species are also very resistant to these kinds of stressors.

Historically, many species have gotten their own Latin names—even without the sexual stage being known. However, in more recent times, some species have gotten their sexual stage identified via molecular methods. One such example is Articulospora tetracladia being identified as the previously described Hymenoscyphus tetracladius.

Identification

Identification of these species is based mainly on spore morphology. Spores usually have tetraradiate, sigmoid, or filamentous shapes. Some important characters for identification include: number, and placement of septa; branches; constrictions at the septa; spiny tips of branches; length and width of branches, with more. The hyphae extends a conidiophore from the substrate and develops a conidia that breaks off into the stream, to find a new substrate, attach, and germinate. These spore morphologies are believed to be specialized to survive stream environments, and attach to specific substrata, which gives them their shapes.