The holly genus, Ilex, has some 400 species, but only one is native to the British Isles. Ilex aquifolium is a medium-sized tree often forming an understory in native oak woodlands. The tree will reach 20m and will grow from suckers hence often forming a clump. The leaves are evergreen, thick with a glossy upper surface and normally with sharp spines. The fertile branches usually carry leaves that are almost spineless. Hollys are dioecious (ie having separate male and female trees) so some trees, the males, will not produce berries. The flowers are small and white and produced in late summer. The female flowers may appear to have stamens but on close inspection these are seen to be shrivelled. Fruit production depends on the presence of both male and female trees and fruit ripens in December. The young stems of holly start off green then turn a silvery grey. The wood is white, very hard, dense and used in fine carpentry and inlay.

The RHS Plant Finder lists 54 cultivars of I. aquifolium in cultivation and 21 cultivars of the hybrid species Ilex x altaclerensis. Three of the commonest cultivars are ‘Golden King’, a gold-edged variegated form which is surprisingly a female and produces berries, ‘Silver Queen’ is silvered variegated and is (you guessed? ) a male producing no berries. ‘Bacciflava’ is a non-variegated form with yellow berries. 

Belfast Botanic Gardens has the species and a number of cultivars. One of the best specimens is on the corner of the path from the Botanic gate to the Palm House. This is a female silver-edged cultivar of Ilex aquifolium, probably ‘Argentea Marginata’

Photos taken in Belfast Botanic Gardens in 2008. Copyright: Friends of Belfast Botanic Gardens.