Characteristics
• eukaryotic
• mostly multicellular, yeasts unicellular
• no locomotion
• sexual & asexual reproduction in most
• heterotrophic by absorption (digestion extracellular)
• > 100,000 species
• saprophytes (also parasites, mutualistic symbionts)
• some pathogenic
• decomposers
• classified by sexual reproduction
• cell walls of chitin (polysaccharide)

Structure
• hyphae – rootlike structures for absorption which collectively form a network, mycelium
• cell walls:
– septate – with cross walls with large pores
– aseptate(coenocytic)– no cross walls; multinucleate
• haustoria – nutrient-absorbing threads that penetrate tissues of host in some parasitic types
• hyphae may grow as fast as 1km/day
• mycelia have haploid nuclei, some dikaryons - 2 separate nuclei that are dissimilar

Fungal mycelia

Cell wall types

Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)

Haustoria

Reproduction
• spores (usu. haploid), diploid in brief sexual reproductive cycles, then meiosis returns these to haploid
• syngamy – nuclear union in fertilization usu. involves some form of conjugation
• usu. asexually in optimal condtions, sexually in harsh conditions

Generalized life cycle

Classification
Division Zygomycota – conjugation fungi
-common molds, incl. Rhizopus stolonifer,
Pilobilus
~ 600 sp. mostly terrestrial in soil or on decaying plants/animals
coenocytic hyphae
-asexually produce sporangia
-sexually by zygosporangia formed during conjugation (+ and – strains fuse)

Zygomycete life cycle

Conjugation

Rhizopus

Pilobilus

Division Ascomycota – sac fungi
~30,000 sp.
-yeasts ( Saccharomyces, Candida ), Peziza
(cup fungus), morels, Ceratocystis ulmi – causes Dutch elm disease
septate hyphae
-asexually by conidia on conidiophores
-sexually by haploid ascospores in asci
-most fungal symbionts in this group

Ascomycete life cycle

Peziza , truffle, morel

Yeast

Penicillium

apothecia

Division Basidiomycota – club fungi
~25,000 sp.
-mushrooms, puffballs, shelf fungi
-produce > 10 billion spores
septate hyphae
-asexually none , or conidia in some
-sexually by basidiospores in basidium

Basidiomycete life cycle

basidiomycetes

Gills of a basidiomycete

Stinkhorn, Phallis impudicus

Amanita (death cap)

Fairy ring

Division Deuteromycota – imperfect fungi
~25,000 sp.
ringworm, athlete’s foot fungus, Arthrobotrys – prey on roundworms in soil
-asexually by conidia
-sexually none observed

Symbioses
1) lichens – algae (filamentous green) –
Chlorophyta or blue green ( cyanobacteria ) & fungus ( ascomycete )
-may reproduce asexually either from fragments or by dispersing tiny airborne starters, soredia

Lichen structure

• each organism also reproduces either sexually or asexually
• alga provides food for fungus, fungus provides moisture, minerals, protection to alga perhaps
• thought to be more of a controlled parasitism , than mutualism

Lichens
• usu. given genus & specific name
• 3 types: a) crustose – crusty b) foliose – leafy c) fruticose – shrubby
*air pollutant indicators

Crustose, fruticose, & folliose lichens

Symbioses
2) mycorrhizae – plant roots & fungus
-plant provides nutrients , fungus provides more surface area to absorb water
-usu. basidiomycetes , may also be ascomycetes or zygomycetes
*found in ~90% of tree species

Benefits of mycorrhizae

Mycorrhizae

Importance
Beneficial:
• decomposers
• food source
• source of antibiotics
• used in food and alcohol industries

Fungal production of an antibiotic

Importance
Harmful:
• decay products
• cause disease
• destroy crops
• spoil food

wheat rust, ergot on rye

pink ear disease of corn