An extremely rare species of fungus, found in four sites in Pembrokeshire, one of which is under the Wildlife Trust of South & West Wales' management, Dowrog Common, has recently been included in a list of the 100 most threatened species in the world.

Willow blister by David Harries

The list, published by the International Union for Conservation of Nature and the Zoological Society of London, was compiled by 8,000 scientists and identifies 100 of the most threatened animals, plants and fungi on the planet.

The willow blister (Cryptomyces maximus) fungus, which is found growing on dead or dying willow twigs, has been recorded in only five sites across the world, four of which are located within Pembrokeshire Coast National Park and the fifth in Sweden.

The Wildlife Trust Officer for Pembrokeshire, Nathan Walton, said: “This species was found on Dowrog Common in 2008 although it was first discovered in the St Davids area in the mid 1980s. It has been known for about 200 years in the UK, although it has never been common".

Willow blister appears as a black fruit body growing through the bark, usually with a conspicuous yellow/orange border and it spreads by wind-borne spores probably infecting only those trees that already have been damaged.

There were only five UK records of this species in the entire 20^th century and it is categorised by the IUCN as critically endangered worldwide.

This extremely rare species has been monitored since being found on Dowrog Common by members of the Pembrokeshire Fungus Recording Network (PFRN) led by County Recorder David Harries, in liaison with the site owners.

In addition to monitoring this species at its known sites, members of the PFRN are constantly looking out for willow blister in likely habitats within the county.

Nathan Walton also said, “This list published by the IUCN highlights the fragile nature of some of our rarest species and the habitats they depend on. Through favourable and sustainable conservation management practices on sites such as Dowrog Common, the hope is that isolated populations are able to grow in their extent".