A branch of the common Ash tree, Fraxinus excelsior, growing near Keswick in Cumbria, UK. The picture was taken in early Summer and shows, below centre, bunches of seeds ( "ash keys") developing from female flowers. The flowers are wind pollinated, and show structural variation from tree to tree. Male and female flowers are sometimes borne within the same inflorescence, but trees may also be entirely male or female, or have branches that are male or female only. In "good" seed years ) this results in copious seed production, with genetic diversity due to cross-pollination between trees. This diversity may enable Ash trees to survive epidemics of disease, such as Ash die-back, Hymenoscyphus pseudoalbidus (formerly known as Chalara fraxinea) first noticed in the UK in 2012 at Ashwellthorpe Wood in Norfolk