This is also known as:

Fagus sylvatica var. heterophylla ‘Aspleniifolia’ or

Fagus sylvatica var. aspleniifolia

The fern-leaved beech is a variety or sport of the common beech. It makes a large tree to 25m as the two fine examples in the Belfast Botanic Garden show. The leaves are very variable, though, unlike the species, dissected to some extent. Fern-leaved beech is said to commonly produce some normal beech leaves, although the Botanic Gardens trees don’t appear to show this characteristic. On the tips of branches some leaves may be very narrow and linear almost like a willow leaf whereas other leaves may look more like an oak leaf – see below. The flowers are the same as the species and bark is smooth and silvery grey also like the species. According to some authorities the fern-leaved beech is a chimaera; that is it combines the tissues of two different plants without being a true genetic hybrid of the two. Usually the inner tissues are of one and the outer tissues are of another – in this case the inner tissues are of the true beech and the outer tissues are of the sport.

NOTE since this was written in 2009, one of the two trees has succumbed to the heart-rotting fungus Ganoderma. Internal imaging of the trunk showed that the tree was partially hollow. In a woodland situation trees with hollow centres may survive for several hundred years, but in a public garden safety issues meant that the tree had to be removed in 2019. The remaining tree is still sound and efforts are underway to propagate from this.