The oakwoods in the ancient kingdom of Meirionnydd in north west Wales are as globally important, and as vulnerable as, some tropical rainforests.
Those are the findings of an 18-month project to survey the area by a team of scientists led by the conservation charity Plantlife.
They found rare populations of mosses, liverworts and lichens that are of national, and international, importance.
Significant proportions of the European, and global, populations of many species are found here
For one species of barnacle lichen (Thelotrema petractoides) it was the first time it had been recorded in Wales.
The woodlands cover an extensive area east of the Snowdonia National Park. They are dominated by sessile oak trees, but also ash, lime, hazel, birch and alder.
This temperate rainforest habitat – part of the so-called Celtic Rainforest – is designated as an Important Plant Area and Special Area for Conservation.
According to Dave Lamacraft, a lower plant and fungi officer for Plantlife, this means they have been identified as being of the "highest botanical importance".
Like other woodlands in the western extremities of Britain and Ireland, the climate is influenced by the proximity to the Atlantic Ocean, making it warm and wet – a 'temperate rainforest'.
"Globally there is much less temperate rainforest than there is tropical rainforest," he said.
It is only found in a handful of locations across the globe, including North America, southern Chile and Japan.
"Thanks to the climate and a long continuity of woodland cover and management in the area, Britain and Ireland's temperate rainforest is home to many species of moss, liverwort and lichen.
"Significant proportions of the European, and global, populations of many species are found here," Lamacraft told BBC Earth.
Among the most important and exciting discoveries they made were lichens.
Lichens are fascinating organisms consisting of two or more partners (a fungus and an alga or a cynobacterium) living symbiotically, that is they all benefit from the partnership.
Lichens take in nutrients from the atmosphere and help feed the forest ecosystem
They are important indicators about the health of our environment.
The team found more colonies of the blackberries-in-custard lichen, first discovered in 2005, making this woodland its only known Welsh site.
This internationally rare species is named because the flask-shaped fruiting bodies (perithecia) grow in blackberry-like clusters and the vegetative body (thallus) can be yellowish like custard.
An even more important find was the rare barnacle lichen Thelotrema petractoides, which has never before been recorded in Wales.
But that's not all, according to Lamacraft.
"The prostrate signal moss is a rare species in Western Europe, found in less than 10 locations in Britain, all of these are in the Meirionnydd Oakwoods," he added.
“The discovery of these new species is a significant find, and highlights the importance of this area of woodland as a rich habitat, home to a diverse range of plants, mosses and lichens,” said Sam Bosanquet, moss and lichen ecologist from Natural Resources Wales.
“Mosses soak up rain, prevent erosion and reduce soil run-off into rivers, and lichens take in nutrients from the atmosphere and help feed the forest ecosystem,” he explained.
The project has confirmed how globally important these pristine woodlands are as a habitat.
But their future is uncertain: they are vulnerable to the effects of climate change, from a lack of grazing that keeps the canopy open and by being overrun by invasive rhododendron plants.
Take part in a week of wildlife-themed events all over Wales during Wales Biodiversity Week, which runs from the 6 - 14 June.
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