Assumed audience
General adult with no formal biology background. The goal is to understand what fungi are and how they work.
What fungi are
Fungi are their own kingdom — not plants, not animals. They are heterotrophs, meaning they cannot photosynthesize. Instead, fungi obtain nutrition by extracellular digestion — secreting enzymes that digest organic matter externally, then absorbing the released nutrients. Their cell walls are made of chitin, not cellulose like plants. Genetically, fungi are more closely related to animals than to plants (see fungal cell biology for more on what makes a fungal cell distinctive).
The fungal body
The main body of most fungi is the mycelium — a network of threadlike cells called hyphae. Hyphae grow at their tips, branch, and can fuse with other hyphae (a process called anastomosis) to form interconnected networks. Hyphae may be divided into cells by cross-walls called septa, or they may be continuous tubes without divisions (a condition called coenocytic). The mycelium grows through its substrate — soil, wood, leaf litter, or a living host — with cytoplasm streaming through the network to distribute nutrients and signals.
Fruiting bodies
The mushroom, bracket, puffball, or truffle that most people recognize as “a fungus” is actually a fruiting body — a temporary reproductive structure. Its job is to produce and disperse spores. The organism itself is the mycelium hidden in the substrate.
Spores and reproduction
Spores are the reproductive units of fungi. They can be produced sexually (involving mating of compatible types) or asexually (clonal). A single fruiting body may release billions of spores. When a spore lands on a suitable substrate, it germinates to produce a new hypha, which grows into a new mycelium.
Major groups
The major phyla of fungi include:
- Ascomycota (sac fungi) — morels, truffles, yeasts, and many molds. They produce spores inside sac-like structures called asci.
- Basidiomycota (club fungi) — mushrooms, brackets, puffballs, rusts, and smuts. They produce spores on club-shaped structures called basidia.
- Other phyla include Zygomycota (bread molds), Chytridiomycota (aquatic fungi with flagellated zoospores), and Glomeromycota (arbuscular mycorrhizal fungi).
For more detail, see Fungal Taxonomy.
Why this matters
Understanding basic fungal biology is prerequisite to understanding their ecological roles, their symbiotic partnerships with plants, and their practical applications in cultivation and fermentation.