THE woodland attached to Usk Castle is to become a proud custodian of Wales's rarest tree. The Leys Whitebeam (sorbus Leyana) has only 17 individual trees growing in the wild, clinging to a limestone cliff in the middle of the Cefn Coed, Merthyr Forest. The tree's site was re-discovered by forester Peter Charlesworth, who started work in the forest in August 1957. Mr Charleworth died in December 2013, and is buried in Usk's Natural Burial Ground. His widow has been presented with 20 saplings of the tree and has chosen to plant some closeto the burial ground to mark Mr Charlesworth's historic discovery. The re-discovery came about when Mr Charlesworth became friendly with a local school teacher who had an interest in the woodlands. The two would often bump into each other on their respective walks, where the teacher would take the opportunity to ask the forester to identify certain species of trees for him. One such tree was the Leys Whitebeam. Unable to identify the tree, Mr Charlesworth took samples and sent them to the Forestry Research Department who confirmed the Leys Whitebeam's identity and rarity. The Carmarthenshire-based National Botanic Garden of Wales shares conservation efforts for the rare Whitebeam with the National Museum Wales and Countryside Council for Wales, researching the tree's genetic origin and ecology in order to conserve them in the wild. Mr Charlesworth retired from his post as Chief Forestry Surveys Officer for England and Wales 23 years ago, preferring to remain out of the spotlight when it came to the interest around the rare tree. However, after an article was published about the tree's cultivation in 2010, the forester approached the National Botanic Garden of Wales' Head of Science and Research, Dr Natasha de Vere, to share the story of his re-discovery and inquire on the work she was undertaking on the specimen. When Mr Charlesworth passed away in December 2013 he had chosen to be laid to rest in the Usk Castle Natural Burial Ground, after spending many years working alongside castle custodian Henry Humphreys in the planting and designing of the castle forests. Mrs Charlesworth contacted Dr de Vere to request a Leys Whitebeam to plant in her husband's memory and was subsequently presented with twenty saplings of various heights to plant, with the clause that they were planted in certain conditions and they agreed to report back every six months on their growth. The significance of the occasion was further implied in that Dr de Vere and the Head Botanic gardener were the only individuals formerly trusted in monitoring and growing the samples outside the Gardens. The trees will be planted in various places around the Castle woodland where Mr Charlesworth had worked. The Leys Whitebeam was first discovered by Augustin Leyes in 1901 on the eastern side of the valley. The trees require very specific growing conditions, preferring plenty of sunlight and self-draining areas and foundations of limestone. Dr Tim Rich, considered the Welsh sorbus expert, confirmed the tree's rarity may be due to reproductive difficulties. "The Leys Whitebeam is the product of a Grey-leaved Whitebeam and the Rowan tree sometime in the last 8,000 years," he said. "As it originated as a cross between two species, it has low fertility and doesn't travel far. "It will be lovely to have a population in the Castle woodlands; they grow well in cultivation." The trees, which grow up to 50ft in height, sport the red berries of the Rowan tree.