Image caption The new mushroom is shaped like a sea sponge and has a musty smell

A new species of mushroom has been named by its discoverers after the cartoon character SpongeBob SquarePants.

The fungus, named Spongiforma squarepantsii by the researchers at San Francisco State University (SFSU), was found during an expedition to the forests of Borneo.

S. squarepantsii is shaped like a sea sponge and, say its discoverers, has a fruity or musty smell.

Details are published in the scientific journal Mycologia.

SpongeBob is the star of an eponymous television cartoon series which began in 1999. The character, who wears a short pair of square, brown trousers, lives in the fictional locality of Bikini Bottom.

The new mushroom is only one of two species that belong in the genus Spongiforma. The other one is found in central Thailand, but differs in its colour and odour.

"We expect that it has a wider range than these two areas," said Professor Dennis E Desjardin, from SFSU, who is a co-author of the scientific paper.

"But perhaps we haven't seen it in more places because we haven't collected it yet in some of the under-explored forests of the region."

Image caption SpongeBob is a sea sponge, but more closely resembles one of the kitchen variety

In addition to its resemblance to a sea sponge, under a scanning electron microscope, the spore-producing area of the fungus looks like a seafloor carpeted in tube sponges, say the researchers.

This further convinced them to name the species after the cartoon character.

The researchers said that Spongiforma's ancestors had the characteristic cap and stem of other mushrooms, but that these features had been lost over time.

The function of the mushroom's stem is to lift the reproductive spores off the ground so that they can be dispersed more easily by the wind and passing animals. The cap protects the spores from drying out.

In its humid home in the forests of Sarawak on Borneo, Spongiforma has taken a different approach to keeping its spores wet.

"It's become gelatinous or rubbery," explained Professor Desjardin. "Its adaptation is to revive very quickly if it dries out, by absorbing very small amounts of moisture from the air."

Professor Desjardin added: "We go to underexplored forests around the world, and we spend months at a time collecting all the mushrooms and focusing on various groups.

"And when we do that type of work, on average, anywhere from 25% to 30% of the species are new to science."