FEARS are growing for the safety of a botanist who has been ­missing for five weeks while on a plant-hunting mission in Vietnam, whose fate his family say they can "only guess at".

Dr Jim Taggart, 82, the botanist father of missing Jamie Taggart, 48, said he believes something untoward has happened to his son, an experienced chronicler of flora around the world.

Privately, there are concerns that if he has had an accident in the Vietnamese jungle he may struggle to survive unaided.

Mr Taggart Jr, who is from Cove and is head of the Linn Botanic Garden in Dunbartonshire - founded by his father in 1971 - was last seen on October 31 leaving his guest house in Sapa on a motorbike taxi. He was heading towards the mountainous region in north Vietnam where he was planning to document plants at high altitude.

The rugged terrain is characterised by dense rainforest with deep gullies.

His father, who embarked on many similar scientific trips while setting up the famous Linn garden near Helensburgh, said yesterday: "The last text message said exactly where he was going. He discussed it with me before. I assumed his mobile phone had failed.

"I don't think he had got lost. Either something happened to him on his first day on the hills or there is some explanation we can only guess at."

He added: "He was found to be missing because he'd left his rucksack in the guest house he was staying in. The guest house, when he didn't come back, phoned the local police. They had a look and didn't see him.

"He had left his passport behind. I understand that when travelling in Vietnam you have to have identity. He might have deliberately left it, knowing my son, in case he lost it on the hill."

Friends of the Linn Botanic Garden have funded private searches in the area at places Mr Taggart had said he planned to investigate. They have hired nine people split into the three teams who are scouring routes Mr Taggart may have taken. They also arranged to have posters distributed in the area

Mr Taggart, who also serves his community as a retained firefighter, had specific locations in mind after his first visit to the region in 2011.

The region being searched is overlooked by the highest peak in Indochina, the spectacular Mount Fansipan, an area also of interest to the searchers.

It is home to some of the world's most exotic plant species including orchids, magnolia and rhododendron.

Fellow botanist Ian Sinclair, 60, his friend of 25 years who last spoke to Mr Taggart on the night he left, said: "The endemics would have looked after him if he had been found.

"There are also workers' huts that they shelter in but [the search teams] have gone round them.

"I lead expeditions like this and it can be a difficult environment."

The Foreign Office said it was aware of the incident, and various people including Lord McFall and Argyll and Bute LibDem MP Alan Reid were also said to be in touch with the authorities.

Prayers have been said for Mr Taggart at Craigrownie Church.

He took over responsibility for Linn Botanic Gardens from his father in 1997. In March this year the attraction was added to Historic Scotland's Inventory of Gardens and Designed Landscapes.

A Scottish Fire and Rescue Service spokesman said many people desperately want to see Mr Taggart return home safely.

Area commander Paul Connelly, the senior officer for Argyll and Bute, said: "This is obviously an extremely difficult time for Jamie's family and friends and we can only hope there will be a positive outcome.

"Jamie has served his community as a dedicated and professional firefighter and is a popular member of a very close-knit and highly experienced team at Cove.

"There are a great many people who desperately want to see him return home safe."

A Foreign and Commonwealth Office spokesman said: "We are aware a British national was reported missing on October 31 whilst in the Sapa Mountain area, Vietnam. We are in close contact with the local authorities and are providing consular assistance to their family at this difficult time."