Silver Leaf Fungus
On downed Alder(Alnus). Saprobic on downed hardwoods, but significantly a plant pathogen of many orchard trees, especially plums and cherries, genus Prunus. It spreads in the wood to leaves and causes characteristic silvering of leaves, usually killing an infected tree. Fertile surface and cap margin starts purple, but eventually progresses to only a purple margin on the fertile surface (depicted)