Tuber indicum

Tuber indicum, commonly known as the Chinese black truffle or the Asian black truffle, is an edible fungus known for its hypogean fruiting bodies, characteristic of the Tuber genus. It is found natively in Himalayan India and parts of China, but has also been found invasively in the United States and Italy. It is sold commercially and often confused with Tuber melanosporum.

Taxonomy
The species was originally described in the Himalayas by Cooke and Massee (1892). It is named “indicum,” from the Latin word for “India,” due to the location of discovery. There are multiple species known as the “Asian Black Truffle,” (T. sinense, T. himalayense, T. formosanum and T. pseudohimalayense) which are often confused with T. indicum. Studies suggest that T. sinense is very likely to be the same species, but this is still up for debate. There is also some discussion that some of the other species listed here are the same, but the evidence is not conclusive.

Description
Known for its dark brown, lumpy or round fruiting bodies commonly known as truffles. They are modified apothecia, also known as stereothecia, and each of their asci produce around 3-5 ellipsoid spores with a variety of ornamentation. The peridium has angular warts, subhexagonal or polygonal in shape. At maturity, the gleba is reddish to purplish black with white veins. The species is genetically diverse and has a lot of morphological variation.

Habitat and ecology
Like other Tuber species, they produce an aroma that attracts animals, leading to the dispersal of their spores through feces. The spores are thick-walled, allowing them to remain intact through the digestive system.

It is a hypogean fungus, with the fruiting bodies growing underground and maturing in winter.

It forms an ectomycorrhizal relationship with various trees such as pines, oaks, and chestnuts (For example, Pinus armandii, Quercus pubescens, and Castanea mollissima ). It is known to successfully form a symbiosis with a wide range of hosts, increasing its invasibility. It is also known to have an effect on the surrounding microbial community. For example, one study shows the effects of the species when growing in symbiosis with Quercus aliena. They noted an increase in richness and diversity of prokaryotes, such as Proteobacteria, Actinobacteria, Bacteroidetes, and Chloroflexi in the surrounding soil. At the same time, there was a decrease in richness and diversity of fungal species. The species can be found natively in Himalayan India and parts of China, as well as invasively in the United States and Italy on trees inoculated with T. melanosporum.

Commerce and use
Because it is nearly identical to T. melanosporum, it is often sold fraudulently to those wishing to purchase the more expensive and highly prized truffle. T. indicum is also valued internationally, but many see it as the inferior species. Its increased popularity has led to habitat destruction.

It has been suggested by one study to screen for certain aromatic compounds in order to prevent fraudulent sale of T. indicum.

The species has also been found growing invasively on trees inoculated with the economically and gastronomically valuable T. melanosporum. Its ability to thrive in non-native soils is a threat to the native species.

Conservation status
The species has been preliminary assessed as Near Threatened on the Global Fungal Red List. It is mainly harvested wild, which has led to overharvesting and habitat destruction as its demand increases. Collection of immature specimens as well as destructive harvesting methods have contributed to their decline.