The American Garden in Dulwich Park is celebrated for its rhododendrons but is also characterised by a large number of birch trees. Birches are also widely planted in the streets of Dulwich, notably in Dovercourt Road, and in several of the streets running from Herne Hill to Half Moon Lane.

The birches in the American Garden are almost all Betula pendula, the silver birch, which is much the most familiar species. There are altogether some 40 species in the northern hemisphere, some found further north than any other trees - it is the national tree of Finland. Birch wood has many valuable uses, notably for plywood and veneers.

Birch trees are easily recognised by their distinctive light-coloured peeling bark, flowers and fruit in the form of catkins (male and female borne on the same tree), smallish leaves, and often weeping branches. By comparison with many other species, they are short-lived, rarely surviving beyond 150 years - so many of those in the American Garden are relatively elderly.

Birch pollen is a potent allergen and affects some 25 per cent of hay fever sufferers. This has made it a less popular choice for street planting in recent years.

In addition to silver birches, other species found in Dulwich include the Himalayan birch, Betula utilis var. jacquemontii, noted for its attractive white bark, and the paper-bark birch, Betula papyrifera, a North American species named for its thin and readily peeling bark.

Dulwich Park tree walk with Daniel Greenwood on Sunday 23 October at 11am

Daniel Greenwood will lead a Dulwich Society tree walk on the theme of tree fungi. Meet inside the Court Lane entrance to Dulwich Park.