This tree was described previously on this website as Carpinus orientalis. Closer examination of the fruit and particularly the bracts around the fruit (see photo below), make it clear that this is a form of the  common hornbeam. The bracts also clearly distinguish it from the  hop hornbeam. The fruit bracts of C. orientalis are not three-lobed. It seems most likely that this is the form of common hornbeam called ‘Asplenifolia’. The other cut-leaved hornbeams C. betulus ‘Incisa’ and C. betulus ‘Quercifolia’ both have smaller leaves than the species. This is a very rare form not listed in most reference sources. It is described in the RHS dictionary of Gardening, but is not mentioned in the Hillier Manual of Trees and Shrubs. This is an attractive tree with some amazing examples of self-grafted branches, quite common in some species and called inosculation – Wikipedia has a description and lots of photos. Our Botanic Gardens tree produces very good autumn colours. It was nominated for a regional Tree of the Year in 2019.

Photos taken in Belfast Botanic Gardens in 2007 and 2019. Copyright: Friends of Belfast Botanic Gardens.