Short answers, pulled from the story.
A fungus is any member of a group of eukaryotic organisms that includes yeasts, molds, and mushrooms, all classified in the biological kingdom Fungi. Fungi are heterotrophs that absorb dissolved organic molecules and perform no photosynthesis, and they carry chitin in their cell walls.
Fungi are no longer classified as plants because they have chitin in their cell walls, lack chloroplasts, and do not photosynthesize. Genetically they are more closely related to animals than to plants, and the two groups diverged around one billion years ago.
Estimates suggest there may be between 2.2 and 3.8 million species of fungi, but only about 148,000 have been described. Over 8,000 species are known to be detrimental to plants and at least 300 can be pathogenic to humans.
A clonal colony of Armillaria solidipes extends over more than 900 hectares, about 3.5 square miles, with an estimated age of nearly 9,000 years. Some individual fungal colonies reach extraordinary dimensions and ages.
Fungi reproduce both asexually and sexually, and a third of all fungi are estimated to use more than one method. Asexual reproduction occurs through conidia or mycelial fragmentation, while sexual reproduction produces spores such as ascospores in ascomycetes and basidiospores in basidiomycetes.
Fungi are used as food in mushrooms and truffles, as a leavening agent for bread, and in fermenting wine, beer, and soy sauce. Since the 1940s they have produced antibiotics such as the penicillins, and they also yield ciclosporin, statins, and the cancer drug lentinan from shiitake mushrooms.
The death cap, Amanita phalloides, is the most common cause of fatal mushroom poisoning, carrying lethal amatoxins. Other dangerous fungi include the ergot fungus Claviceps purpurea, which caused epidemics of ergotism known as St Anthony's Fire, and Aspergillus species that produce carcinogenic aflatoxins.