Flora Celtica is no ordinary granny. She comes in wearing a leather jacket and dancing to the sound of Mel C’s “Things can never be the same again”. She has a mobile telephone, a boyfriend and a suitcase full of secrets which must not get into the wrong hands or else the future of life in rural Scotland may be in danger.

Whatever you do, she warns her granddaughter, Jules, before rushing off for a motorcycle lesson, don’t open that suitcase.

What happens next is pure pantomime and the primary school children love it. This was not what they expected when their teacher sent for the Royal Botanic Garden Edinburgh pack in preparation for the Flora Celtica roadshow.

“I thought it would be boring,” writes one of the children from Airidhantuim Primary on Lewis a few weeks after the roadshow visited the western isle, “just people talking about flowers.” Instead, writes another, “I found that learning could be fun.”

The message of the roadshow is that we need the wild plants of Scotland as much as we have always done and we must act quickly to save our heritage. Wild plants and wild places are disappearing and the people who know how to traditionally use them are dying out too.

The first hour of the show is a play with plenty of audience participation; the last half-hour gets children creating advertisements to sell plant products without destroying the environment. Schools apply for the teaching pack in advance and ideally children learn that different plants grow in different habitats.

The show prompts a new understanding of science and new respect for what we can learn from old people. But surprise and entertainment are the essence. “We slip the education in when the kids aren’t looking,” says Julie Jones, an education officer for the Royal Botanic Garden Edinburgh who plays Jules.

“The trouble is,” says Naomi Knight, a fellow education officer who plays Flora, “when we came to that bit about sustainability I found it hard to keep the teachery note out of my voice.” The solution was to make the children discover the idea for themselves.

Granny’s suitcase is a touch of inspiration. In 49 out of the 50 Highlands and islands schools visited by the roadshow, children willingly help Jules break her promise to Granny. They dive in to discover the wonders it contains: willow for baskets and aspirin, bog myrtle for midge repellant, heather for rope, seaweed for jelly and toothpaste, urine (“Yuk!”) for fixing plant dyes and a few other surprises.

But in one small island school, the 14 pupils politely declined when Jules asked if they would help her open Granny’s suitcase. “No,” they solemnly shook their heads, “Granny said we mustn’t.”

It was a difficult moment for Jules, well aware of her responsibilities as adult and teacher. “In character I had to persuade them to come with me, but inside I had to work hard to overcome the feeling that I was being really bad.”

After the children open the suitcase, Granny gives Jules a scolding and in the process makes the point hat we must respect the plants we need to survive.

There is not a trace of a “teachery note” as the school, teachers included, join Jules and Granny in the “Sustainability Rap”.

“Plant products are really hip You take care they don’t go zip Sus-tain-abil-ity Is no big tease Ecofriendly?

Oh yes please!” The advantage of the educational roadshow is that it brings new information direct to schools who may not have the money or time to travel to museums or botanic gardens. It is also a timely reminder that, in our technical age, actual experience is still the most inspiring way to learn. “Children get a lot from books and they enjoy downloading information from the Internet but there is nothing to beat the personal touch,” says Christine Darroch, headteacher of Keills Primary on Islay, speaking for many involved in the project.

Flora Celtica takes an unusually human view of plants. Behind this imaginative and highly ambitious scheme are two young botanists who probably spend as much time working with people as they do studying plants.

William Milliken, an associate of the Royal Botanic Garden Edinburgh, moves between Scotland and remote reaches of the Amazon, where he is involved in helping to persuade younger members of the Yannomami that they have much to learn from their elders about traditional uses of plants.

Sam Bridgewater, from RBGE’s tropical biology department, works with farmers in the savannah of Brazil, studying the medical properties of the fruits and nuts they have harvested for centuries. Now he also gathers knowledge from crofters in the Highlands and islands of Scotland, where people have likewise harvested natural resources for centuries.

“It’s the same issue,” says Mr Milliken. “Traditional knowledge is disappearing fast all over the world but it still has potential for development. We need to increase public understanding of the value of plants in people’s lives. We felt we could achieve more by working in our own backyard.”

The result is Flora Celtica Scotland 2000: part science, part folklore, part social history, part theatre and wholly infectious. Ultimately Flora Celtica aims to document and disseminate knowledge of native plant uses throughout the Celtic countries of Europe, linking Wales, Cornwall, the Isle of Man, Ireland, Brittany, Spain, Portugal and Norway. But it begins in Scotland with combined sponsorship from the Millennium Festival Scotland Fund, businesses and charitable trusts.

It also depends on public support. Mr Milliken and Mr Bridgewater started by appealing for public information. Research led them through written records to the spoken words of crofters, bards and healers still living in the western highlands and islands. Now they want to spread the heritage. Hence the roadshow.

A Flora Celtica exhibition (including children’s work) runs at the Exhibition Hall, Royal Botanic Garden Edinburgh until July 30 before touring Scotland for the rest of the year.www.rbge.org.ukresearchcelticaNext term, a new roadshow visits Benmore Botanic Garden in Argyll, September 11-15.Contact the education department, Royal Botanic Garden Edinburgh, tel 0131 552 7171