By Jemima Laing
Take a look at our film of the rare lichen
You've heard of finding a needle in a haystack but how about finding a tiny lichen in an estate some 10 miles square?
While it might not give rise to a terribly catchy turn of phrase, spotting this extremely rare lichen is no lesser feat.
But Devon lichenologist Barbara Benfield did just that when she discovered the millimetre-wide plant at Killerton in February 2010.
The lichen, Micarea parva, is so rare that even the Natural History Museum doesn't have an example of it.
The lichen is practically invisible to the naked eye
Barbara said her discovery at the hill fort at the National Trust property near Exeter was a "big surprise", especially as it's almost invisible to the naked eye.
About 18,000 species of lichen have been discovered in the world, over 1,800 occur in Britain - 900 of them in Devon.
"I've not seen it before, ever, and to find it in my local patch was quite exciting," she said.
"On the whole the Killerton volcanic rocks are too dry for most lichens," said Barbara.
"The record considerably extends the lichen's known range in the UK and indicates that important discoveries can still be found locally."
Rather than being one type of organism, a lichen is a partnership between a fungus and an alga.
These form such a close relationship that they appear as a single individual and this individual looks completely different from either the fungus or the alga by itself.
They have no leaves, stems or roots, but like plants the algal partner makes food using energy from sunlight.
They are also excellent barometers of air quality and add another layer of diversity and beauty to the environment with their different colours and shapes.
"It's barely a millimetre across so it's really difficult to find so I don't think it's going to be a big tourist attraction!" said Ed Nicholson from the National Trust.
"But it's here and if people want to know where it is we'll be happy to show them."