Fungal Forms
Fungal forms are fungi of unknown or multiple affinities, including yeasts, conidial fungi, mycorrhizae, and lichens.
Lichens
Mutualistic relationship between three organisms
An ascomycete fungus is the heterotroph forming the matrix, absorbing water and minerals
A unicellular alga or cyanobacterium serves as the autotrophic partner
Lichens with cyanobacterium symbiote can fix nitrogen
(Newly discovered) A unicellular basidiomycete yeast, embedded in the lichen cortex or "skin", that produced chemicals to protect the entire organism
Mostly ascomycetes, ~13,000 spp.
Polyphyletic group, lichens evolved at least five times
Slow growing: 1-2mm per year
Ecologically important:
pioneer species on rocks, barren soils as well as bark
extremely widespread (arctic to tropics, wet to dry)
great indicators of air pollution since they are sensitive to sulfur and nitrogen
Forms: crustose, foliose, fruticose
Yeasts
Unicellular fungi belonging to Ascomycota, Basidiomycota, or Mucoromycota
Reproduce through budding (asexual)
Rarely conduct sexual reproduction
Commercially used as a source of ethanol or CO2
Crucial in the production of wine, beer, and bread
Recently discovered basidiomycete yeasts serve as a 3rd partner in lichens (see lichens - below)
Above: Magnified image of yeast cells
Conidial Fungi
Artificial assemblage of asexual fungi (15,000 spp.)
Once called Deuteromycetes or “Imperfect” Fungi
Reproduce asexually through conidia (asexual spores)
Mostly ascomycetes, some basidiomycetes, and mucoromycetes
Include Athlete's Foot and Penicillium
Above: Conidia of Penicillium
Mycorrhizae
A mutualistic relationship between plant roots and a fungus
Plants provide the products of photosynthesis (carbohydrates)
Fungi provide water and minerals
Few roots hairs grow on plant roots since the fungus is much more efficient at absorbing water and minerals
More than 90% of all plant families examined have this relationship
75% of all seed plants are assumed to have mycorrhizae
There are two types of mycorrhizae: endomycorrhizae and ectomycorrhizae
Endomycorrhizae
Fungi invade the root cells
Also called vascular-arbuscular mycorrhizae (VAM)
These are usually glomeromycete
In nature, these are more common than ectomycorrhizae
Ectomycorrhizae
These fungi surround the plant root as a fungal sheath
They produce special hyphae called haustoria which penetrate root cells
These fungi tend to be basidiomycetes, but sometimes ascomycetes
Sometimes these fungi will produce "fairy rings" of basidioma around the tree in which they colonize
Above: microscopic example of endomycorrhizae in cortical cells of root
Above: Ectomycorrhizae of Amanita on a Larix root
Above: macroscopic example of ectomycorrhizae on roots
Additional Resources
Inoculating soil with mycorrhizal fungi can increase plant yield by up to 40% (Phys.org 29Nov2023)
Mycorrhizae may help store more than a third of fossil fuel emissions (ZME Science 6Jun2023;
Hawkins et al. 2023. Mycorrhizal mycelium as a global carbon pool
Are Trees Talking Underground? For Scientists, It's In Dispute (NY Times 7Nov2022)
The Idea That Trees Talk to Cooperate Is Misleading (SciAm 19Jul2021)
Lichens are a symbiosis of three (not two) partners (Science 2016)
Plants force fungal partners to behave fairly (University of Zurich 2016)
Researchers evolve a multicellular yeast in the lab in 2 months (Ratcliff et al. 2011)
Mycorrhizae may not be mutually beneficial (IIASA 2014)
On Fungi and Forest Diversity (In Defense of Plants 2017)
Article: Coevolution of roots and mycorrhizae (Brundrett 2002)