Halfway up the Upper Broadwalk you’ll find Wales’s rarest tree – Sorbus leyana (Ley’s Whitebeam). There are only 17 in the wild, each clinging onto steep limestone cliff sides in the Brecon Beacons.

Was Ley’s Whitebeam  more widely distributed in the past? No-one really knows. It was only discovered in 1896 and not named until 1934.

Why is it so rare? Three thoughts. It may have only evolved recently. It can’t cope with grazing by animals. It doesn’t reproduce easily.

How do we stop it becoming extinct? Ex-situ conservation – we are establishing a population of trees at the Garden as a safety net in case the wild ones die. These have been propagated from the wild trees by grafting.

In-situ conservation - with the National Museum Wales and Countryside Council for Wales, we are researching the tree’s genetic origin and ecology. This will help us to conserve them in the wild. Ley’s Whitebeam flowers May – June, and fruits from August – October.

There’s also a Ley’s Whitebeam in our Welsh Rare Plants bed behind the Theatr Botanica, and we have recently planted a Sorbus Grove , next to our Living Machine display (number 27 on the map). This collection of British whitebeams is part of our conservation programme. It includes the 6 species that are only found in Wales, several of which are threatened with extinction.  By keeping this collection, our horticulturists learn how to propagate and grow these trees and create back-up populations which could one day be planted in the wild. At the same time, botanists have easy access to plant material for identifying the differences between species (many of which are inaccessible in the wild) and researching the genetic origin and ecology of these trees. The photo shows  Professor Charles Stirton, the Garden’s first Director, planting a tree named after himself, Sorbus stirtoniana, in the Sorbus Grove in 2010.