The unknown world of mushrooms
Only about 4 percent of the mushrooms are scientifically recorded, according to a study by scientists from the Botanical Garden and Botanical Museum of the Free University of Berlin as well as the London Royal Botanic Gardens, Kew and the Natural History Museum. Around 2.2 to 3.8 million types of mushrooms are said to exist worldwide. Mushrooms thus form the second largest kingdom of organisms after animals, because the mushrooms surpass the diversity of plants by about 6-10 times. At least 18 times more mushroom types exist than are currently known. The research results were published in the current issue of the specialist journal "Microbiology Spectrum".
One of the big questions in biology has now been dealt with. In the past, speculations ranged from just over half a million to over 5 million types of mushrooms worldwide. Only 120,000 types of mushrooms are currently known and scientifically described. This corresponds to only about 3 to 8 percent of the estimated global mushroom diversity. Over 2 to 3 million types of mushrooms can still be discovered and described. The fungi are thus the least studied of the three large organism kingdoms: while around 80% of the estimated 390,000 species are cataloged in plants, around 20% of the estimated 7 million in animals.
The detection of the still unknown mushrooms is a monumental task for the researchers, since currently only about 1500 new types of mushrooms are described each year. It would take another 1,500 to 2,500 years to describe all as yet unknown types of mushrooms. Or ten times as many specialists to complete this task within the next two centuries. Due to habitat destruction and unsustainable management, however, the mushroom diversity continues to decline globally: many species die out before they are discovered.
For the current estimate, the researchers combined three estimation methods. First, they evaluated the latest research data, which are essentially based on DNA sequencing methods. Just by analyzing the so-called DNA bar coding, an average of about 10 previously unknown species were discovered in supposedly known mushroom types (such as the toadstool or the chanterelle). The already known 120,000 types of mushrooms could therefore correspond to up to 1.2 million species.
Second, the researchers used analyzes of environmental samples, such as soil or water. All existing organisms are recorded using new DNA sequencing methods. The researchers suspect at least 1 million additional, unknown mushroom species worldwide, totaling around 2.2 million. Thirdly, studies at selected locations, where all plant and mushroom types were systematically recorded, showed that an average of 9.8 mushroom types occur per plant type. With a projected number of 390,000 plant species worldwide, this alternative estimation method results in a total of 3.8 million mushroom species.
The researchers suspect many undescribed types of fungi in so-called hotspots such as the tropics, little-studied habitats (including symbiotic lichens and insects) and in raw material from natural history collections.
Fungi are present in all ecosystems, even in the sea. The realm of mushrooms includes unicellular organisms such as baker's yeast as well as the macroscopic toadstool or lichen fungus. According to current knowledge, mushrooms are more closely related to animals than to plants, but traditionally mushrooms are often treated further in botany; until the late 20th century they were even counted among plants.
Mushrooms combine typical characteristics of animals and plants. Like plants, they are stuck but, unlike plants, do not perform photosynthesis; instead, they feed on organic substances from their environment. As a storage substance, they form the polysaccharide glycogen typical of animals (and not a starch typical of plants). Fungus cells usually have a cell wall that is typical for plant cells, but this is made up of chitin, which is known in the animal kingdom. Many fungi decompose dead organic material and are therefore of central ecological importance in the nutrient cycle.
Fungi living in symbiosis can be found in most plants (e.g. trees and orchids) as well as in lichens (a symbiosis of fungi with algae or cyanobacteria). Parasitic fungi are important pathogens in plants, animals and also humans. In addition to delicacies such as truffles, mushrooms are the basis for everyday foods such as bread and cheese, alcoholic beverages, and medicines such as antibiotics (penicillin). (sb, pm)
Hawksworth D., Lücking R. 2017. Fungal Diversity Revisited: 2.2 to 3.8 million species.
Microbiol Spectrum 5 (4): FUNK-0052-2016.