History and Evolution of Fungi

• Fungi first appeared approximately 1.5 billion years ago.
• Fungi share a common ancestor with animals, making them more closely related to animals than plants.
• The history of fungi illustrates their adaptation to diverse environments and their ecological importance.

Early Evolutionary Stages

• The earliest fungi were likely simple, water-dwelling organisms.
• Early fungi probably resembled modern chytrids.
• Chytrids typically live in aquatic environments and possess spores with tails for swimming.
• Early fungi played a crucial role in facilitating the transition of plants onto land by forming partnerships with early land plants.

Adaptation to Terrestrial Life

• Fungi developed adaptations for survival on land, including a strong cell wall made of chitin.
• Chitin constitutes the hard outer shells of insects and other arthropods.
• The chitinous cell wall protects against desiccation and other environmental stressors.

Diversification and Modern Groups

• Fungi diversified into several main groups, each with unique characteristics and ecological roles.
• The diversification resulted in the wide variety of fungal types observed today, differing in shapes, reproduction methods, and environmental interactions.

Major Groups of Fungi

• Fungi are classified into main groups based on morphology, reproduction, and genetic makeup.

Chytridiomycota (Chytrids)

• Chytrids are the most basal fungal group.
• They generally live in water and produce motile spores.
• Chytrids break down dead organic matter in aquatic environments and can cause diseases in amphibians.
• Chytrids are usually very simple, often unicellular or composed of a few cells without internal walls.
• They reproduce both sexually and asexually, often forming sporangia that release swimming spores.

Zygomycota (Zygomycetes)

• Zygomycetes primarily inhabit terrestrial environments and decompose dead plants and animals.
• Sexual reproduction involves the formation of a zygosporangium, a thick-walled structure containing developing fungi.
• Zygomycetes have long, tube-like structures without internal walls and produce non-motile spores.
• Sexual reproduction involves the fusion of specialized fungal parts to form a zygosporangium. Asexual reproduction occurs through structures that release spores.

Ascomycota (Ascomycetes)

• Ascomycetes represent one of the largest and most diverse fungal groups.
• They produce spores within sac-like structures called asci.
• Ascomycetes include yeasts, molds, and morels.
• Ascomycetes have long, tube-like structures with internal walls and form asci to hold their spores.
• Sexual reproduction involves the formation of asci, while asexual reproduction often produces spores called conidia.

Basidiomycota (Basidiomycetes)

• Basidiomycetes produce spores on structures called basidia.
• This group includes mushrooms, puffballs, and bracket fungi.
• They are crucial for decomposing dead organic matter and forming symbiotic relationships with plant roots.
• Basidiomycetes have long, tube-like structures with internal walls and create basidia to hold their spores.
• Sexual reproduction involves the formation of basidia and basidiospores; asexual reproduction may involve conidia.

Glomeromycota (Glomeromycetes)

• Glomeromycetes are a smaller group that forms symbiotic relationships with plant roots.
• These partnerships facilitate nutrient uptake from the soil for plants.
• Glomeromycetes have long, tube-like structures without internal walls and form specialized structures inside plant roots.
• They primarily reproduce asexually by producing spores.

Basal Lineages

• Some fungi do not fit neatly into the main groups including insect-infecting fungi (Entomophthoromycota) and some aquatic fungi (Blastocladiomycota).

Fungal Classification

• Fungal classification is based on morphology, reproduction, and genetic information.
• Historically, classification relied heavily on morphological characteristics.
• Genetic information is now used to better understand relationships between different fungi.

Morphological Classification

• Classifying fungi based on their physical appearance.
• Key morphological features include: hyphal structure, reproductive structures, and spore appearance.

Reproductive Classification

• Fungi are grouped based on their methods of reproduction.
• Sexual reproduction involves the fusion of specialized fungal parts.
• Asexual reproduction involves spore production without fusion.

Genetic Classification

• Modern classification uses genetic material to determine fungal relationships.
• Genetic analysis has revealed new relationships and led to reclassification of some fungi.