Christos Mousafidis, a police officer on the Greek-Albanian border, mainly deals with drug trafficking and illegal immigration. But this year he is grappling with a different kind of crime: herb smuggling.

"Villagers alerted us to it," he said. "Something was going on."

Climbing for about an hour and a half up to an altitude of some 1,300 metres (4,000 feet), "we discovered a camp in the middle of the mountains and more than a dozen Albanian pickers at work," Mousafidis said.

The makeshift camp of nylon and plastic tents had several days' worth of provisions.

Mules stood ready to transport the harvest -- a staggering 4.5 tonnes of a type of sage -- to market along mountain paths to neighbouring Albania.

In August, some less discreet pickers were arrested in the centre of Tripoli, a city in the southern Peloponnese, with a lorry load of 200 kilogrammes (440 pounds) of wild oregano and "mountain tea", a very popular infusion in Greece.

Though pickers are well aware of the profits to be had from wild Greek plants, the boon has been largely overlooked by the legitimate agricultural sector.

"We have a remarkable biodiversity. Of 7,500 plant species (in Greece), 20 percent are aromatic and pharmaceutical herbs including dozens of endemic species. But they are not grown very much," said Eleni Maloupa, a researcher at the Greek Agricultural Organisation DEMETRA.

Greek exports are well behind the European leaders in the sector -- Germany, France, Bulgaria, Italy and Poland.

But the demand is there.

Illegal pickers were paid 20 euro cents a kilo (24 US cents for 2.2 pounds) for herbs harvested this year on the border with Albania, which were sold on for four euros a kilo by a middle-man in Italy, according to Mousafidis.

- Clandestine trade 'hurts flora' -

Whether the end use was culinary or pharmaceutical has not been determined, but the trade was brisk enough that another group was caught in the act at the same place a few weeks later.

The clandestine trade "hurts the flora because the cutting is done without precautions", says forestry official Soulatana Giannakoupolo.

Maloupa, who runs a botanical garden in northern Greece that specialises in aromatic herbs, also lamented the uncontrolled sale of the herbs.

Kostas Economakis, an expert on mountain teas who formerly worked at the National Institute of Agronomics Research, said: "It's so much lost profit because these herbs are sold for less when they are not certified."

At the market in northern Salonika, half of the plants sold in sachets were not cultivated but picked wild on the mountainside, Maloupa said.

But the tide is turning. Last year Greek growers set up an association while the government launched a "national catalogue" serving as a scientific reference on the plants.

"More and more young people or entrepreneurs are turning towards... aromatic and pharmaceutical plants," Maloupa said.

Since 2012 Greek mountain tea has been available in ready-to-drink form with the brand name "Tuvunu" and sold in San Francisco, New York and Paris.

Developed in northeastern Greece between Xanthi and Komotini, Tuvunu is "a mixture of 17 kinds of mountain tea, honey, lemon and nothing else," says the boss, Demetri Chriss.

To ensure quality, the business persuaded farmers in the region to alternate the crop with the tobacco they grow.

"Now we have agreements with 300 farmers all over Greece. And we turn down proposals from those who want to send us wild herbs picked in the mountains."