The Number Is A Range
Taxonomy — Fungi
The Number Is a Range
Headlines said Costa Rica may have more than 40,000 species of fungi. The study behind them gives a range, and 40,000 is its top.
In March 2026 a team of researchers published a study of Costa Rica’s fungi, and the news reported that the country may have more than 40,000 species. That number is in the study. It is the highest of a range of estimates, and the study does not give it as the answer.
The study began with what the country already holds: nearly 80,000 specimens kept in fungaria. A fungarium is a collection of preserved fungi, dried and labelled the way books are shelved in a library. A specimen is one labelled sample. The country has worked at documenting its biodiversity for the past 35 years, and the records reach back more than a century.
Before this study, the published literature listed 5,676 species of fungi in Costa Rica. The collections hold species that the literature does not list. Adding them brings the known count to 6,789, about a fifth more.
How many are there in all? The study uses estimators, statistical methods that infer a total from how often each species has been found. They disagree. Estimators that stay inside the collections give between 3,918 and 4,445, because the collections hold only part of what is known. Methods that do not rely on collections can also count dark taxa: fungi known only from DNA read out of soil samples, never collected and never described. Those methods can reach far higher. The range in the study runs from 4,155 to 40,373, a spread of nearly tenfold, and the headline took the top. A range this wide is the honest answer to a question the data cannot yet settle.
Set against the larger estimates, the collections look thin. The species fully identified in the country’s collections might account for as little as 7 percent of the country’s potential fungal diversity. The known count of 6,789 is already more than twice the number recorded in the collections themselves, and the authors conclude that a vast number of species are likely still undescribed.
Most of what is on the shelves has been found almost never. Taxa, meaning named groups of fungi, recorded five times or fewer make up about 90 percent of the total, and 65 percent were recorded exactly once. The authors say this reflects true rarity, under-sampling, or both. A species seen once cannot be told apart from a species that is merely hard to find. That is one reason the estimates are wide.
More collecting would help less than one might expect. The study’s curve suggests that doubling the collecting effort, with the same methods, would add only 25.9 percent more species. The authors stress a second remedy: many specimens are named only to genus, the group above species, and they say curating these is likely to reveal new species and first records for the country.
The collecting has been uneven. The southern Talamanca range, the Osa Peninsula and parts of central Guanacaste are well sampled. The Pacific slope of the Guanacaste mountains, the Nicoya Peninsula and the whole Central Pacific region are among the least sampled, though the authors say they offer habitat suited to fungi. The gaps in the records show where people looked. They do not show that nothing grows elsewhere.
A type specimen is the sample that fixes the meaning of a species name, and it serves as the permanent reference. 81 percent of type specimens from Costa Rican material are kept abroad. Rules require a duplicate to be deposited in the national collections, and the authors found several recent cases where that was not done. Of all Costa Rican specimens, 83 percent sit in just two national collections, known as CR and USJ.
The headline said more than 40,000 fungi. The study gives a range from about 4,000 to 40,000. Nearly two-thirds of the taxa on record were found only once. Doubling the collecting would add about a quarter. Fully identified species in the collections might be as little as 7 percent of the potential total. Four in five type specimens are abroad. A species count is a statement about how much has been looked for.