Fungi are opportunistic organisms that resemble both plants and animals but are actually neither. Fungi:
- Can exist as a single cell (like some yeasts) or as a multi-cell organism.
- Are heterotrophic: like animals, fungi live off other organic material. Most plants are autotrophic, producing their own food via photosynthesis.
- Can reproduce by teleomorphic (sexual) or anamorphic (asexual) means, through fragmentation or by producing spores. The spores themselves can be sexual or asexual.
- Some fungi change from teleomorphs to anamorphs, adapting as environmental conditions around them change.
- Some fungi reproduce both sexually and asexually (“perfect fungi”). “Imperfect fungi” can only reproduce asexually.
- Digest their food externally, by excreting enzymes onto organic matter, then ingesting the matter back into their cells. Animals ingest food first, then digest it internally.
- Can be saprophytic (feeding on dead or dying material). Parasitic fungi obtain nutrition from a living host. Some, Armillaria mellea for example, transition from parasitic back to saprophytic, feeding on the organism it killed.
There are about 148 thousand identified species of fungi; a 2011 article suggests the total number is 5.1 million species.
Related reading:
*= in LHL print collection
Microfungi on land plants : an identification handbook by 
Morfometrii︠a︡ i sistematika gribov by 
Illustrated Genera of Smut Fungi by 
Yeasts : characteristics and identification by 
