This May, London’s parks and streets are alive with the subtle charms of the Sorbus family—whitebeams, rowans, and wild service trees—each hiding stories of rarity, hybridisation, and botanical intrigue. From the creamy blossoms of our native whitebeam (found in just 17 unique British forms, some clinging to existence as single trees) to the self-seeding rowan, now a city staple, these trees defy easy identification. Venture to Larks Wood in Chingford, and you’ll find the elusive wild service tree, its name borrowed by pubs (though rarely its true likeness) and even the Prime Minister’s countryside retreat.
But the real wonders are the oddities: the Bastard Service Tree (a rowan-whitebeam hybrid), the Swedish whitebeam (a pollution-resistant street star), and the Wye Valley’s exclusive Sorbus x vagensis. Hunt down the pear-fruited Service Tree in Crystal Palace Park or admire the metallic-barked Sorbus aria ‘Beissneri’—a living sculpture.
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Whitebeams, Rowans and Service Trees
All these trees are in the genus Sorbus, of which there are over one hundred different species. Rowans have pinnate leaves with many leaflets, whitebeams have oval leaves and wild service trees have leaves like maples. As all of them interbreed, producing many intermediates, the range of leaf shape can be very confusing.
Our native Whitebeam Sorbus aria is now covered in bunches of large, clotted-cream coloured flowers, which will deteriorate quickly. There are seventeen different local races of this tree in Britain, some of which are designated as species in their own right. They often exist in tiny populations, sometimes just a single tree e.g. the Rock whitebeam S. rupicola; and others such as S. bristoliensis only exists as a small population in the Avon Gorge in Bristol and nowhere else in the world. The Least whitebeam S. minima is restricted to just a couple of places on a limestone scar near Crickhowell in Wales. Others, such as S. anglica and S. lancastriensis are found in only one or two areas of the West Country and Lancashire respectively.
Rowan trees S. aucuparia used to be rare as a wild tree in London, but due to being recommended for small gardens it is now planted extensively and is often found self-seeded. The rowan hybridises with the whitebeam to produce the Bastard Service tree S. x thuringiaca. This is the most common of several similar hybrids to be seen in London’s streets. The Swedish whitebeam S x intermedia is another which is popular due to its resistance to aerial pollution.
The Wild Service tree or Chequers tree S. torminalis is one of our rarer native trees. It can still be found easily enough in Larks Wood, Chingford. It is most famous for lending its name to the prime minister’s weekend retreat in the Chilterns, where it still exists naturally. Many a public house has a fraudulent inn sign with a picture of a chequerboard rather than of this tree. It hybridises with the whitebeam to produce S x vagensis which is only found in the Wye Valley.
Even more confusingly, there is another Service tree S. domestica which was originally also thought to be native due to one single ancient tree in the Wyre forest. It has many leaflets like a rowan and produces small pear-shaped fruits, which like medlars can be eaten when bletted. Three of these trees can be found in Crystal Palace Park farmyard and one in Wanstead High Street Recreation Ground.
The leaves of all these trees can vary from the elliptical leaf of the white beam to the completely different pinnate leaf of the rowan. Consequently confident identification can be difficult and fruits may make it easier in the autumn. The berries also vary from scarlet in the case of the rowan to white, pink, green and crimson in the many different garden Sorbus spp. In gardens, it is the enormously large-leaved S. aria ‘majestica’ that is worth seeking out and S. aria ‘Beissneri’ with its unforgettable shiny, metallic, copper-coloured bark.
Tree Flowers
From last month, many magnolias, crab apples, cherries and maples are still to be seen in flower. Magnolias tend to be noticed less this month as their leaves are now obscuring their flowers. However, some of the most beautiful magnolias with crimson centres e.g. Magnolia sieboldii are just coming into flower. Others, with tight, upright lily-shaped flowers e.g. M. lilliflora may also becoming more common . The tallest of them all, M. acuminata, the Cucumber tree, has metallic blue and yellow flowers. One planted at Kew in the early eighteenth century is now over twenty-five metres in height.
Other tree flowers often noticed now include red and white horse chestnuts, yellow and pink buckeyes, the Judas tree, kuwhai, foxglove tree, handkerchief tree, medlar and laburnum . A white rather than the usual purple-flowered Judas tree can be seen at Fulham Palace. Adam’s laburnum Laburnocytisus Adamii can be found in the City of Westminster cemetery at Hanwell. It is a chimaera, curiously producing distinctly separate bunches of purple and yellow flowers on the same tree. The purple flowers originate from a purple broom Cytisus purpureus, which was grafted onto a laburnum by a Monsieur Adam at his home in Paris in 1825. The tissues of both plants amalgamated perfectly to produce this oddity.
There are also still many oriental cherries in flower, although quite a number seem to disappear as crab apples reach their best. Cultivated crab apples (Malus spp.) are some of the most attractive of all tree flowers, going from bright red though pink to white and often just a mixture of all these colours. Other than Kew and Wisley, a fine collection of flowering trees this month can also be enjoyed in Cannizaro Park.
