These two closely-related trees are both members of the birch family which, along with birch itself, also contains alder and hazel. All have alternate, simple leaves with toothed edges and all bear male and female catkins on the same tree.
Hornbeam (Carpinus betulus) is a native tree which has a predominantly south-eastern distribution in this country. It is an indicator species of ancient woodland and Dulwich is lucky enough to have it in the older parts of Dulwich Woods. It behaves there in a way typical of it in its natural habitat: as a graceful, rather retiring, component of the woodland rather than being a dominating feature. In other woods around London, however, it can impose itself more. Epping Forest, for example, abounds in hornbeam, some of which are pollard relics of the days when common fuelwood rights existed there. Hornbeam is first-rate as firewood because its wood is extremely hard, as suggested by its name: Horn because its wood is as hard as horn and beam from Baum, the German word for tree.
Hornbeam and its most commonly-planted cultivar, the fastigiate hornbeam (var.Fastigiata), also occur quite frequently in Dulwich as planted trees. Fastigiate refers to a plant with upright branches forming a narrow outline. The cultivar lives up to its name when young but it tends to thicken in middle-age, when its outline can resemble a large round balloon rather than the trim shape of its youth. If you want to see both trees together then a good place is Lovers Walk (also known as Grove Walk), where both have been planted, by the path and in the adjoining meadow to the south.
As to identification, in winter hornbeam’s buds are distinctive. They are oval, pointed, curved and held closely to the stem. This gives them a bent appearance from above, and makes them look like little mice running up the twig. Older books usually compare hornbeam leaves in summer to those of the elm, from which they differ by lacking the elm-leaf’s asymmetric base; more modern ones to those of the beech, from which they differ by having serrated edges and more pronounced veins. A fully mature hornbeam has a beautiful fluted, silvery-grey trunk. Nowhere was this better displayed than on the
splendid specimen that used to stand at the southern end of Dulwich Village, just before the roundabout on the east side. That tree, alas, had to be cut down a few years back.
The two hornbeams on College Road, on either side of the entrance to Frank Dixon Way, are just beginning to show signs of this fluting, particularly the southernmost one. The fastigiate hornbeams in Frank Dixon Way itself are already showing marked Falstaffian tendencies, despite being youngish trees.
Hop-hornbeam Ostrya carpinifolia, or European hop-hornbeam to give it its full name, is a much less common tree. It is a native of Southern Europe and Asia Minor and was introduced to Britain in 1724. There are many small differences between it and hornbeam but the most effective way of distinguishing between the two is to wait until their fruits have dried out in summer. The fruit of both trees occurs in distinctive hanging clusters, but that of hop-hornbeam is enclosed within a papery, inflated husk which makes it look very much like that produced by the hop plant. Hence the common name which, as is often the case, is much more usefully descriptive than the scientific one. Dulwich has two mature examples of hop-hornbeam: one in the Village burial ground, northern end, and the other at the south-eastern end of Frank Dixon Way, just before it meets Dulwich Common. Pleasingly, a third, younger, hop-hornbeam has been planted very near to the spot in Dulwich Village where its close relation, the magnificent hornbeam referred to in the previous paragraph, once stood. So it will be easy to keep an eye on the development of this most interesting tree.
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