Fern Leaved Beech, Fagus sylvatica 'Asplenifolia', is a grafted tree first cultivated in 1804 that often has both the common beech leaves and the cut-leaved 'fern' shaped ones on the same tree.
You may know the one in the park at Todmorden but my photos also show one near Dobroyd Castle. It was planted about 1869 by Edward Kemp (who probably planted the one in Todmorden park). Notice the huge bulge near the base where the tree was grafted.
Centre Vale Park