Fungal Diversity Revisited: 2.2 to 3.8 Million Species

Abstract

The question of how many species of Fungi there are has occasioned much speculation, with figures mostly posited from around half a million to 10 million, and in one extreme case even a sizable portion of the spectacular number of 1 trillion. Here we examine new evidence from various sources to derive an updated estimate of global fungal diversity. The rates and patterns in the description of new species from the 1750s show no sign of approaching an asymptote and even accelerated in the 2010s after the advent of molecular approaches to species delimitation. Species recognition studies of (semi-)cryptic species hidden in morpho-species complexes suggest a weighted average ratio of about an order of magnitude for the number of species recognized after and before such studies. New evidence also comes from extrapolations of plant:fungus ratios, with information now being generated from environmental sequence studies, including comparisons of molecular and fieldwork data from the same sites. We further draw attention to undescribed species awaiting discovery in biodiversity hot spots in the tropics, little-explored habitats (such as lichen-inhabiting fungi), and material in collections awaiting study. We conclude that the commonly cited estimate of 1.5 million species is conservative and that the actual range is properly estimated at 2.2 to 3.8 million. With 120,000 currently accepted species, it appears that at best just 8%, and in the worst case scenario just 3%, are named so far. Improved estimates hinge particularly on reliable statistical and phylogenetic approaches to analyze the rapidly increasing amount of environmental sequence data.

FIGURE 1

Numbers of newly introduced species names of fungi for each decade from 1750 to 2010. Based on data from the Index Fungorum database provided by P. M. Kirk.

FIGURE 2

Numbers of newly introduced species names of fungi for each year from 1975 to 2015. Note that the data for 2015 were incomplete when this work went to press. Based on data from the Index Fungorum database provided by P. M. Kirk.

FIGURE 3

Growth in the total catalogued number of species names of fungi by decade from 1750 compared with the global number of accepted species. Based on figures adopted in the 10 editions of Ainsworth & Bisby’s Dictionary of the Fungi for 1943–2008 and data in the Index Fungorum and Species Fungorum (Catalogue of Life) databases provided by P. M. Kirk.