The hydnoid fungi are a group of fungi in the Basidiomycota with basidiocarps (fruit bodies) producing spores on pendant, tooth-like or spine-like projections. They are colloquially called tooth fungi. Originally such fungi were referred to the genus Hydnum ("hydnoid" means Hydnum-like), but it is now known that not all hydnoid species are closely related.
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Hydnum was one of the original genera created by Linnaeus in his Species Plantarum of 1753. It contained all species of fungi with fruit bodies bearing pendant, tooth-like projections. Subsequent authors described around 900 species in the genus.[1] With increasing use of the microscope, it became clear that not all tooth fungi were closely related and most Hydnum species were gradually moved to other genera. The Dutch mycologist Rudolph Arnold Maas Geesteranus paid particular attention to the group, producing a series of papers reviewing the taxonomy of hydnoid fungi.[2] [3][4][5]
The original genus Hydnum is still current, but is now restricted to the type species, Hydnum repandum, and its relatives in the family Hydnaceae. Other species originally described in Hydnum have been reassigned to various genera in various families, including the Auriscalpiaceae, Bankeraceae, Hericiaceae, Hydnodontaceae, Hymenochaetaceae, Lachnocladiaceae, Lentariaceae, Meruliaceae, Phanerochaetaceae, Schizoporaceae, and Thelephoraceae.[1]
The fruit bodies of hydnoid fungi are diverse, but all produce their spores on the surface of pendant, tooth-like or spine-like projections.
Some terrestrial species producing fruit bodies with a pileus (cap) and stipe (stem) are collectively known as the stipitate hydnoid fungi and are often studied as a group because of their ecological similarity. The species concerned are now referred to the genera Bankera, Hydnellum, Phellodon, and Sarcodon. All are ectomycorrhizal, belong in the Bankeraceae, and are considered to be indicator species of old, species-rich forests. In Europe, at least, many are of conservation concern and feature on national or regional red lists of threatened fungal species. In the United Kingdom the stipitate hydnoid fungi have been given Biodiversity Action Plan status[6] which has increased interest in the group and has generated funding to be put into survey work[7][8] and other research.[9][10]
Species of Hydnum, as well as some tropical species of Beenakia, Climacodon and Terenodon, are also stipitate and hydnoid, but have different ecological requirements.
The largest group of fungi formerly placed in the genus Hydnum are wood-rotting species, forming patch-like fruit bodies on dead attached branches, logs, stumps, and fallen wood. Species with small "teeth" (just a millimetre or so long) are sometimes described as "odontioid" (tooth-like). These resupinate hydnoid species are not treated collectively, but form part of the corticioid fungi. Genera that have hydnoid or odontioid representatives include Dentipellis, Dentocorticium, Mycoacia, Odonticium, Radulodon, Sarcodontia, and Steccherinum.
Other hydnoid fungi include a group of conspicuous, wood-rotting species with long spines belonging to the genus Hericium, often referred to as "tooth fungi".[11] Several bracket fungi have teeth instead of pores, including species of Climacodon and Echinodontium. The ear-pick fungus and other species of Auriscalpium are hydnoid, as is the odd jelly fungus Pseudohydnum gelatinosum.