The seed had grown into a 2ft-high sapling when it was pulled up

The Southern Beech was grown from seed collected in its native Tasmania in 2000 by botanists from the Kew Gardens base in West Sussex.

It was discovered that the 2ft-high sapling had been dug up last week in a routine inspection at Wakehurst Place.

Attempts to plant or sell the tree are likely to fail because it has suffered root damage, needs special care, and is easily recognisable, Kew Gardens said.

Experts say the thief is unlikely to dare to show it in a public place.

This was the only one that survived here Wakehurst Place spokesman

The thieves took the tree but damaged the roots when they pulled it up, leaving only the two cages in place that protected it from wild animals.

Wakehurst Place, which holds the national Nothofagus collection and is the site of Kew's �80m seed bank, said it was the only recorded example of a Nothofagus gunnii in the country.

"This was the only one that survived here from those brought back five years ago," a spokesman said.

Tasmanian marvel

"While we still have thousands of other wonderful trees producing glorious autumn colour, it is so selfish of the thief to have deprived others of enjoying it.

"Now the tree has been lost, not only for people to come and admire, but also to researchers who wanted to know more about it."

He added: "In its native Tasmania, the species provides magnificent autumn colour when most of the trees there are evergreen, and everyone there has their favourite spot from which to view this iconic tree."

The tree was being monitored for the interaction between the soil and its roots, because it is so hard to grow in England.

Sussex Police said it was "an unusual theft" and that if the crime had been reported, officers would be investigating as normal.

Nothofagus gunni is said to be the only cold weather deciduous tree or shrub in Australia.

It has broad, light green leaves and main veins extending to the gaps between the leaves' rounded teeth.