Reproduction in fungi can be either asexual or sexual; many species use both methods. The structures that develop in different reproductive stages of fungi also serve as an important tool for identification, especially sporangia and conidia.

Asexual reproduction occurs in three steps: (1) cell division, (2) fragmentation of hyphae, and (3) spore formation. In cell division, a fungal cell divides to form two daughter cells. This reproduction requires only the building of a new cell wall through the middle of the parent cell, a process called trans verse fission. As cell division builds hyphae stretching longer and longer, some cells break off from the septate hyphae at the cell wall interfaces. The single hyphal cells become spores called arthrospores and find another place to begin growing or germinate.

Certain fungi develop derivations on simple hyphal fragmentation. In some species, hyphae stop growing as fi laments at a certain point and begin producing a chain of spores at the tip of a branched bundle of hyphae. The branched bundle is called a conidiophore, and the spores that it grows and releases into the air are conidiophores. Aspergillus mold forms a round conidiophore that holds hundreds of small circular spores.

Other fungi develop sacs full of spores. For example, a sac called a sporangium might form at the tip of a hypha and contain hundreds of sporangiospores, which escape when the sac ruptures. The fungus Rhizopus uses this method to create new organisms. Other fungi, such as Candida, make some sacs called chlamydospores within the hyphae rather than at the ends and other sacs at the hyphal tips (terminal chlamydospores). The thick cell wall of the hyphae surrounds each chlamydospore, which breaks off the hypha as a single piece. Fungi that use none of these techniques for making and spreading spores may simply grow buds off their hyphae that also bud into spores. These spores are called blastospores, and as do chlamydospores, sporangiospores, and chlamydospores, they disperse into the air several inches to a mile (1.6 km) or more from their origin. Only arthrospores depend less on airborne travel and spread mainly through the soil or other places where the parent mold grows.

Sexual reproduction involves the union of gametes that each contains half of a complementary chromosome, a haploid structure. Some fungi produce both male and female gametes on different hyphae in the same mycelium; some fungi produce the gametes on different mycelia. Two compatible gametes that meet fuse their cytoplasm and then fuse their nuclei. The nuclear fusion creates a zygote containing the full chromosome, a diploid structure. Zygotes develop further into the type of spores that are characteristic of the parent fungi. Thus, fungi of Ascomycota form ascospores, Zygomycota develop zygospores, and Basidiomycota produce basidiospores.

The stage of a fungus’s life cycle represents more than an academic curiosity. The structure associated with certain reproduction phases often correlates with the diseases caused by fungi, called mycoses. For example, the yeast Candida usually exists in its single-celled form and causes no harm when living on the human body. When Candida cells develop hyphae, however, they can invade the skin to start troublesome infections.

In most fungal reproduction, the vegetative mycelium participates in both sexual and asexual reproduction. Zygomycete fungi,  such as Rhizopus, shown here, construct a sporangium that releases spores into the air. The spores germinate to form a new  vegetative structure after they settle on the ground.