239,180 fungal species hypotheses in UNITE

UNITE is a database of ITS sequences maintained by the University of Tartu, built on the region used as the fungal barcode. In version 10.0, updated on 25 March 2026, it holds 3,846,536 ITS sequences drawn from UNITE and the international nucleotide databases, and 239,180 fungal species hypotheses delimited at a 1.0 per cent gap.

A species hypothesis is not a species in the nomenclatural sense. It is a group of sequences similar enough to be treated as one operational unit, given its own code and a DOI. Clusters are computed at several thresholds — from 0.5 to 3.0 per cent — so the number of units depends on which one is chosen. The figure above is for the one per cent threshold, and without that detail it cannot be compared with anything.

The comparison with formally described species is the interesting part. Nomenclatural registers list more than 150,000 fungal names — UNITE holds tens of thousands of units more, and most of them have no scientific name at all. They come from environmental sequences — soil, water, air, the tissues of other organisms. A large share of fungal diversity is therefore known as a sequence long before anyone sees a fruiting body.

The number is a snapshot of one release and changes with every new version as sequences accumulate and clusters are recomputed. Every earlier release is preserved, however, and a hypothesis code carries its version number, so an identification made years ago can still be resolved. That is a rare and valuable property: the database grows without invalidating its own history.

A sequence cluster is not a formally described species

UNITE version 10.0 of 25 March 2026 held 3,846,536 ITS sequences and 239,180 fungal species hypotheses at the 1% inter-cluster threshold. A species hypothesis, carrying a stable SH identifier, groups sequences for ecological analysis and comparison among datasets. It may correspond to one described species, several close species, or a lineage without a formal name.

The threshold is part of the result: a different similarity level produces a different number of clusters. Subtracting 155,000 names from 239,180 hypotheses therefore does not yield a count of “new species.” These are two systems organising different forms of evidence.