But the moss man of the National University of Singapore is immune to stares and snide remarks.

'My job is to build up the data on different moss species and where they can be found,' said Associate Professor Tan, a 50-year-old Filipino who joined the department of biological sciences in 1997.

The world holds an estimated 15,000 moss species, 2,000 of them in tropical South-east Asia.

Small is beautiful to Prof Tan, who has spent more than 20 years studying this simplest and most ancient group of land plants.

He said: 'There are unique compounds in moss that can be found nowhere else. These have not been studied in detail, and could one day be made into drugs to treat diseases.'

Associate Professor Peter Ng, director of the Raffles Museum of Biodiversity Research, said Prof Tan's work was a stepping stone in conservation efforts and the search for certain disease cures.

He said: 'Mosses have been around for hundreds of millions of years, and have stayed the course of history regardless of what has been thrown at them. Let's find out their special tricks and use them to help human survival.'

Prof Tan has compiled online databases on regional moss species and endangered species elsewhere. The Raffles Museum has collected 2,000 samples from the region that researchers can use for reference.

Mosses, he said, are the safest food for an untrained person lost in the jungle.

'None are known to be poisonous. They taste quite bitter, but they could sustain you,' he said.

One of only four moss experts in South-east Asia, he has blazed trails in some of the most remote spots in the world, from the Gobi Desert to the rainforests of Papua New Guinea, in his hunt for new species.

During a month-long trip to eastern Siberia in 1997, sponsored by National Geographic, he and his team had to take a helicopter into a mountainous region because there were no roads.

The team found 280 species there, including two new ones, and presented a report to the Russian government, which was compiling a list of rare plant and animal species, with the aim of turning the area into a national park.

Such trips are not without their thrills. In Papua New Guinea, Prof Tan saw two warring tribes battling with bows and flaming arrows. In Siberia, his raft overturned in a river and he almost drowned in the freezing water before struggling to shore.

'Sometimes, when I look up from a sample I've been studying, I come face to face with a snake. And once, I fell down a cliff and broke my arm in six places,' he recalled.

So passionate is he about moss that he is never without a small magnifying glass strapped around his neck - a must for examining species that may be only a few millimetres long - and a canvas bag, scraper and other collecting paraphernalia.

Prof Tan, who has three species of mosses and liverworts named after him, said he became interested in plants as a child going on hiking trips in the Philippines. That youthful enthusiasm has yet to wane.

'When I make a big discovery, I jump up and down and hug my colleagues. Then it's time to pack up and go home, because you know you won't do anything better that day.'