Most fungi are capable of asexual and sexual reproduction. Asexual reproduction is by fragmentation or spore formation. Those that reproduce sexually produce gametes in specialized areas of the hyphae called gametangia. The gametes may be released to fuse into spores elsewhere, or the gametangia themselves may fuse. In some cases dikaryons [ di = two, karyo = nucleus], which are found only among fungi, result when unspecialized hyphae fuse but their nuclei remain distinct for part of the life cycle.
Unlike algae or plants, fungi lack the chlorophyll necessary for photosynthesis and must therefore live as parasites or saprobes (see parasite). Typically they release digestive enzymes onto a food source, partially dissolving it to make the necessary organic or inorganic nutrients available. Some parasitic types obtain their food directly from the cells of a living food source. Some types of fungi are involved in symbiotic relationships, for example, lichens (a combination of a fungus and a green alga or a cyanobacterium) and the mycorrhizae (symbiosis between a fungus and the roots of a vascular plant).
Some fungi are pathogenic to humans and other animals. Such diseases are called mycoses or fungal infections. Some molds, in particular, release toxic chemicals called mycotoxins that can result in poisoning or death. Various fungi can also cause serious damage to fruit harvests and other crops (see diseases of plants).