Backstone Bank and Baal Hill Woods one side valley, there is a small population of small-leaved lime, "Tilia cordata", which occurs here close to its northern limit and at an unusually high altitude. On base-rich soils, the woodland typically consists of ash, "Fraxinus excelsior", and wych elm, "Ulmus glabra", over an understorey of hazel, "Corylus avellana", and bird cherry, "Prunus padus", and a rich ground flora that includes lady-fern, "Athyrium filix-femina", male fern, "Dryopteris filix-mas", and hard shield-fern, "Polystichum aculeatum". On more acid soils, sessile oak, "Quercus petraea", and birch, "Betula sp.", are dominant. The under-storey, of hazel, holly, "Ilex aquifolium", rowan, "Sorbus aucuparia", and hawthorn,
Sorbus mougeotii which differs only in slightly broader leaves. It is also closely related to "Sorbus intermedia" (Swedish whitebeam), which differs in having the leaves grey-white below and more deeply lobed, with the lobes spreading rather than forward-pointing, the fruit oval and less bright red, and in forming a stouter tree with a single trunk and more horizontal branching. All are tetraploid apomictic species which breed true without pollination, and ultimately of hybrid origin between "Sorbus aria" and "Sorbus aucuparia". It is widely grown as an ornamental tree in northern Europe, though usually unrecognised, misidentified as "Sorbus intermedia". Although described in 1858,