The growth form for most fungi is a network of thread-like cells called hyphae (sing. hypha). En masse, the network of hyphae is called a mycelium.
Figure \(\PageIndex{1}\): The mycelium of a fungus fans out across a woody substrate, branching successively. Photo by Dr Mary Gillham Archive Project, CC BY 2.0, via Wikimedia Commons.Figure \(\PageIndex{2}\): In the image above, there are several long, transparent, thread-like structures (hyphae). In this particular fungus, the hyphae are divided into compartments by cross walls called septa (septum, singular). There are four arrows in the image, each one is pointing to a septum. Photo by Maria Morrow, CC-BY-NC.
Spores
Fungi reproduce by making haploid spores. Spores can be formed through asexual or sexual reproduction. The method by which fungi produce spores via sexual reproduction is a useful characteristic for grouping them into different phyla. The shape, size, number, color, and texture of spores are all often useful characteristics in identifying fungi to a more specific level.
Figure \(\PageIndex{3}\): Spores produced by Psilocybe cyanescens, Basidiomycota (first) and Tuber gibbosum, Ascomycota (second). Photos by Alan Rockefeller, CC-BY-NC.
Molds
"Molds" are filamentous fungi producing spores (usually asexually). Many different groups of fungi produce molds, including many of the former Zygomycota, Ascomycota, and Basidiomycota.
Figure \(\PageIndex{4}\): The image above shows a petri plate with at least 10 mold colonies. Each colony has a central point that would have started with a single, haploid spore. This spore would germinate and grow outward, producing more spores asexually by mitosis. Photo by Maria Morrow, CC-BY-NC.Figure \(\PageIndex{5}\): This diagram shows a forking structure called a conidiophore with many single cells being produced in rows at the ends of these forks. These cells are haploid conidia, spores produced by mitosis in Ascomycete and Basidiomycete molds. Artwork by Nikki Harris, CC-BY-NC.
Video \(\PageIndex{1}\): In this epic digital rendering (cue electric guitar on synthesizer), a fungus in the genus Aspergillus is producing tall, lollipop-like conidiophores. From these, chains of conidia are formed. As the conidiophores sway and bump into each other, the conidia are dispersed into the air.
Yeasts
Normally, fungi have a filamentous form. However, many groups within Kingdom Fungi produce yeasts. Yeasts are unicellular fungi. Though some yeasts can reproduce sexually, they are usually found reproducing asexually via a process called budding. In budding, the parent yeast cell replicates its nucleus by mitosis. A small protrusion forms in the cell wall and the new nucleus and cytoplasm are pushed into this protrusion or "bud". A wall forms between the bud and the parent cell, leaving a bud scar on the parent cell. The new yeast cell can then grow to a mature size.
Figure \(\PageIndex{6}\): In the diagram above, a yeast cell reproduces by budding. On the far left, we see the parent yeast cell (the nucleus is labeled). Moving from left to right, the yeast cell forms a protrusion, then produces a copy of the nucleus by mitosis. In the next frame, a cell wall has formed between the protrustion (bud) and the parent cell and they have physically separated. In the final frame, the two yeast cells are equal in size and genetically identical, but the parent cell can be identified by the presence of a circular bud scar. Artwork by Nikki Harris, CC-BY-NC.
