It is the most mysterious wildflower in Britain, the strangest, the rarest, the hardest to see, and it was given up for lost. But like a wandering phantom, the ghost orchid has reappeared.

After an absence of 23 years, during which it was declared extinct, this pale, diminutive flower, the most enigmatic of all Britain's wild plants, rematerialised last autumn in an oak wood in Herefordshire.

Its sighting, initially kept a close secret, has electrified the British botanical community. Forget your black tulip. This has been British botany's holy grail, searched for annually and ardently by a small army of enthusiasts for more than two decades, but never found.

Its eventual rediscovery was due to the painstaking detective work of an amateur botanist, Mark Jannink, who identified 10 possible sites in the Welsh borders and visited them regularly throughout the summer, until on 20 September he found a single example of Epigogium aphyllum, bearing a single white flower on a white stem only five centimetres tall.

The plant was so unobtrusive that it was invisible from a few yards away. On spotting it, Mr Jannink exclaimed: "Hello you – so there you are!"

There had been no previous ghost orchid sighting in Britain since a single plant was found in Buckinghamshire in 1986. It was officially declared extinct in Britain's Red Data List in 2005.

Mr Jannink, 42, who runs a motorbike company in Malvern, Worcestershire, and has been a wildflower enthusiast since his childhood, said yesterday: "To be honest, I was ready to give up, and the feeling when I saw it was of relief more than anything. It was the following day I felt the euphoria."

The species is hard to find because it does not appear every year and behaves more like a fungus than a flower, according to the naturalist Peter Marren, author of Britain's Rare Flowers.

"It has no green leaves," Mr Marren said. "It doesn't depend on photosynthesis at all, and it doesn't manufacture its own food.

"Instead, the food is manufactured for it by a fungus on its roots. It lives largely underground; in fact it can live underground without flowering properly for years on end, and it only flowers when conditions are just right."

Mr Marren added that when it does bloom, the ghost orchid flowers in the thick leaf-mould in the darkest parts of the woodland, where there is no other vegetation.

"It's the hardest British flower to see," he said. "It looks extraordinary. It produces these flowers without chlorophyll which in the dim light look like ghosts, and if you shine a torch beam on them they appear to be translucent white in the pitch darkness, almost like a photographic negative."

He described the rediscovery as "terrific news", adding: "It's one of the most fascinating flowers."

A remarkable irony of the rediscovery is that last September, in the very month in which the plant was found – but before the finding was made public – the ghost orchid was chosen as the symbol of a new conservation campaign because of its presumed extinction.

Plantlife, the wild flower charity, called its new manifesto for preventing wild flowers from disappearing The Ghost Orchid Declaration.

"The rediscovery of a single ghost orchid is wonderful news," one of the declaration's authors, Dr Trevor Dines, said yesterday.

My audience with a rare orchid

In mystique, there is only one other flower in the whole of the British flora with which the ghost orchid, Epigogium aphyllum, can be compared, and that is another orchid species – the lady's slipper.

For more than half a century, only a single plant of this purple and yellow bloom existed and during its flowering season it was guarded around the clock at its secret location. Orchid fanciers had reduced it to the very brink of extinction.