Tuber melanosporum Vittad. - Périgord Truffle

Tuber melanosporum Vittad. - Perigord Truffle

Taxonomy

Phylum: Ascomycota

Class: Pezizomycetes

Order: Pezizales

Family: Tuberaceae

Tuber melanosporum, the Périgord Black Truffle, grows in mycorrhizal relationship with the root systems of oak and hazelnut trees. At a farmers' market price of about 1000 Euros per kg (2010 prices) and a retail price of three or four times that amount, along with Beluga caviar this is one of the world's most expensive luxury foods and, most mycophages would agree, also one of the very finest. Forgive us, therefore, if what follows refers only to the mycological features of this subterranean mushroom...

Tuber melanosporum Vittad. - Perigord Truffle -- cross-section view

Truffles are ascomycetes, which shoot their spores from flasks (asci, singular ascus)... but underground? Surely that can't work! The answer is that these kinds of fungi rely on animals digging them up and eating them. Even after the spores have passed through the gut of an animal and been excreted, they are able to produce a new mycelium, which is vital for their reproduction in a new area, provided they can find and link up with the root system of a suitable tree species.

Cut a truffle and it gives off a most distinctive (but un-mushroomy) smell. Pigs, dogs and other creatures with noses more sensitive than our own do not need the truffles to be cut open or even dug up: they can smell them from above ground. This is why professional truffle hunters use either pigs or dogs to help them locate this source of 'black gold'. Pictures: Moi-meme (public domain)

Tuber melanosporum, the famous Périgord Truffle, and its Italian rival Tuber magnatum, the Piedmont Truffle, have a scent that mimics a male pig's sex hormone. That is why in the past professional truffle hunters used female pigs to help find these hidden treasures. Nowadays dogs have replaced pigs as the truffle hunter's preferred companion. (Well, the people who do this work for a living have to cover a lot of ground, and they must have to take their assistants with them in their cars or vans as they travel from home to forest to customer premises.)

Identification Guide

Description

There is no point in trying to describe the shape of a truffle: they are the ultimate in shapelessness. Blobs, sometimes more or less spherical but quite often multi-lobed, the outer surface of a Périgord Black Truffle is dark brown to black, covered in small crazed polygonal sections with shallow rivers between them (not unlike limestone pavement, but less regular in size and not aligned in any logical way.)

Inside, the dark spore-bearing material is marbled by white membranes, again in a random wandering way rather than any regular pattern.

Dimensions

Typically a few cm across and weighing 50 to 200g each, but exceptional specimens weighing over 1kg each are found.

Spores

Elliptical, 29 – 55 x 2 2– 35µm; covered in spines 2 - 4µm long; light brown to mid brown in mass.

Habitat

Mainly under oak trees, particularly Cork Oaks, in southern Europe - France, Portugal, Spain and Italy in particular. Also known to occur under Hazel, Hornbeam and very occasionally pines.

Season

Late summer, autumn and, in the far south, through the winter.

Occurrence

Being subterranean, these mushrooms are rarely seen by people walking in woodlands, and so their occurrence is a matter of conjecture (or of commercial secrecy if you are a truffle merchant!).

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2011.

Dennis, R.W.G. (1981). British Ascomycetes; Lubrecht & Cramer; ISBN: 3768205525.

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.