Jamie Taggart, 48, who runs the Linn Botanic Gardens in Dunbartonshire, founded by his 82-year-old father Dr Jim Taggart, has not been seen since he left his guest house in the mountain region of Sapa, north of Hanoi, on October 31, heading west on a motorbike taxi.
Mr Taggart Jr may have been looking to document and photograph plants at a greater altitude than he had explored before.
His father confirmed his son is missing and no trace has been found. He said yesterday: "My son Jamie has disappeared when on a botanical excursion to North Vietnam. Presently he is being actively searched for, so far without result of any kind."
Friends of the Linn Botanic Gardens are also funding separate searches along routes they believed he would have travelled - areas he did not reach while on a previous visit to the district in 2011.
Ian Sinclair, 60, who has known Mr Taggart Jr for 25 years and spoke to him on the night before he left Scotland, said yesterday: "We just want to get as much information out about Jamie as possible."
His passport and rucksack were at his guesthouse.
The area is not considered dangerous for travellers and it is thought local people would have sheltered the botanist had they found him in distress.
The dense temperate rain forest, however, is described as difficult terrain and concerns are growing for his welfare.
The Scots-funded search teams made up of local experts will travel from Tram Ton to Cong Troi, or Heaven's Gate, Lai Chau and then Khoang Village.
The whole journey will take five days.
Mr Taggart Sr bought the Linn Villa in 1971 and set up the famous garden by sourcing plants from China, Peru and the Himalayas. His son, a retained firefighter who is not married, took over the garden, an Historic Scotland property, in 1997.
A spokesman for the Foreign and Commonwealth Office said: "We are aware that a British national was reported missing on October 31 while 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."