True truffles (Tuber species) are distributed only in the North Temperate region. They occur across the warmer parts of this region with moderate climate, centred in Europe at latitude 44° N, extending their range out between latitudes 38° and 50° N, and declining further north to 60° N, in southern Scandinavia and Canada and south to 30° N, in North Africa, southwest China and northern Mexico.
In the 230 years since the genus (Tuber 1780) was formally recognised, about 100 species have been identified in Europe (60), Asia (10) and North America (30), with a smaller number of varieties of some of the species, throughout their range.
The full distribution and exact number of truffle species are not known since they are not readily visible due to their invisible subterranean habitat. Records are only available for locations where they have been collected. New species are continuing to be discovered and named and the total may be double the current figure. It is estimated that Tuber contains a minimum of 180 species. Ongoing scientific studies on the phylogeny of truffles rely heavily on study of field-collected specimens, however, species boundaries and species concepts are not clearly defined for most species.
Truffle species are endemic to specific (northern) continents, and where they occur in both Eurasia and North America, it is the consequence of human introduction, often accidentally through forestry activities or sometimes through deliberate cultivation. The ancestor of truffles was originally present in Europe or was widespread in Eurasia. The epicentre for the best truffles is in the region between Provence in south-eastern France and Piedmont in north-western Italy. Truffle were known for as long in Asia as in Europe, but the local species were of lesser quality and they were less appreciated there.
Chinese: mogu=mushroom, songlu=truffle
Korean: beoseos=mushroom, teulwipeul=truffle
Japanese: kinoko=mushroom, toryufu=truffle
physical map of Europe (image source: wikipedia)
Other minor genera of the truffle family that do not have culinary importance occur in the Southern Hemisphere.
Truffles grow only in well-drained, calcareous, alkaline soils with a minimum of pH7.5 and up to pH9, ideally of pH8-8.5 for maturation, in mixed flowering tree-conifer forests at the foothills of mountains, variously at low-altitudes (300-400m), mid-altitudes (600-700m) and high-altitudes (1000-1200m) according to species. Altitude seems to be of significance in their presence and they are generally found in higher grounds ranging from 100 – 1000m above sea level.
In Europe, truffles occur along the Apennines in Italy; the Massif Central in France, and along the southern Pyrenees in Spain.
In North Africa, along the Atlas Mountains in Morocco, especially in cedar tree habitats.
In China, on the north-eastern slopes of the Himalayas, where they occur at very high altitudes (2000-2400m).
In North America, along the Appalachians in the east, and the Cascades in the West.
The chalky or limestone soil need to have not more than 40% clay, sand or loam. If the soil is acidic or not sufficiently alkaline, other competing fungi will establish on the rootlets instead. Where the truffles grow they usually occur in a circular formation around the base of the host tree about 1.5 to 2m away, and are attached to the rootlets of trees to a depth of about 20 to 30 cm below ground, but large specimens can be found as deep as 70 or 80 cm.
Truffles grow from low altitudes in foothill and montane zones in Europe, North Africa and North America, to the high altitude alpine zone in China, and nearing the snow zone in Tibet. Most truffle species grow in the intermediate montane zone in mixed conifer-broadleaf forests.
Foothill zone (Tierra caliente) – 400 to 800m
– characterised by deciduous forests with abundant and dense vegetation
Hosts: pedunculate oak (Quercus robur), durmast oak (Quercus petraea), sessile oak (Quercus sessilifolia), holm oak (Quercus ilex), downy oak (Quercus pubescens) and cork oak (Quercus suber); sweet chestnut (Castanea sativa), European beech (Fagus sylvatica), Italian alder (Alnus cordata), hornbeam (Carpinus betulus), hop-hornbeam (Ostrya carpinifolia) and small-leaved linden (Tilia cordata); black pine (Pinus nigra), maritime pine (Pinus pinaster) and yew (Taxus baccata). Grape (Vitis spp.) crop limit, around 600 m
Montane zone (Tierra templada) – 800 to 1400m
– characterised by coniferous forests either of pure conifers or mixed conifers and broadleaf
Hosts: durmast oak (Quercus petraea), sessile oak (Quercus sessilifolia) and holm oak (Quercus ilex); sweet chestnut (Castanea sativa) and European beech (Fagus sylvatica); black pine (Pinus nigra), maritime pine (Pinus pinaster), silver fir (Abies alba) and European spruce (Picea abies).
Alpine zone (Tierra helada) – 1400 to 2400m
– characterised by shrubs and sporadic dwarf trees with close carpet meadows
Hosts: forest pine (Pinus sylvestris), European spruce (Picea abies), Swiss Pine (Pinus cembra) and European Larch (Larix decidua), limit, 2,000m.
Snow zone (Tierra nevada) – 2400 to 3200m
– characterised by extremely few plants with snow cover throughout most of the year