Rowans, Service Trees & Whitebeams
What are they?
These woody members of the rose family (Rosaceae) were until recently all members of the genus Sorbus, a fairly large and diverse group of small trees. More recently, taxonomists have split Sorbus into a number of new genera, which helps to break them into more identifiable groups. This page contains both native plants and species introduced from abroad as ornamentals and amenity plants. There is great variation in the appearance of these species, with some having compound leaves (and sometimes known as mountan ash) and some having simple leaves with pale undersides - the whitebeams. In addition, there are a number of species with intermediate appearance, as well as some that have almost maple-like leaves (service-trees). Despite all this leaf variation, there is a similarity in the appearance of the flowers and fruits that will help to identify a plant as belonging to this group.
Where are they found?
This diverse group contains species that are common, native plants of heathland and copses, as well as a number of introduced species that are most likely to be found as old garden relics or planted as street trees in urban areas.
Identification
Most species can be identified by details of the leaves, but fruits can be important for some species, as well as whether the buds are sticky or not.
Common Rowan Sorbus aucuparia
Native. Common on heaths and commons on sandy soils but also widely planted elsewhere. Flowers May to June, small, but carried in many-branched, flattened heads. Fruits 7-12mm across, orange-red.
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Service-tree Cormus domestica
(Sorbus domestica) Native to southern Europe and the Caucasus region. Rare, but occasionally planted as an amenity tree in urban areas. Flowers April to June. A medium-sized tree, to 25m in height. Leaves compound with 13-21 leaflets. Fruits large for this group, rather like a cross between a crab apple and pear, up to 5cm in length, yellowish to orange-red.
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Common Whitebeam Aria edulis
(Sorbus aria) Native elsewhere in the UK but only an introduction in East Anglia. Quite widely planted as a street tree and perhaps occasionally self-seeding. Flowers May to June, small, but carried in many-branched, flattened heads. Fruits 10-15mm across, red with pale freckles. Many planted trees are of the cultivar 'Lutescens' which has noticeably pale leaves due to a thick covering of white hairs, especially when young. The opening leaves appear in an upright cluster and can be mistaken for magnolia flowers from a distance.
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Swedish Whitebeam Scandosorbus intermedia
(Sorbus intermedia) Introduced from northern Europe. Quite widely planted as a street tree and perhaps occasionally self-seeding. Flowers May to June, small, but carried in many-branched, flattened heads. Fruits 11-15mm across, orange-red with only one or two pale freckles. Leaves whitish beneath, relatively broad and deeply lobed.
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Bastard Service-tree Hedlundia thuringiaca
(Sorbus thuringiaca) Introduced from mainland Europe. Occasionally planted as an amenity tree, most often as the narrow-growing cultivar 'Fastigiata'. Flowers May to June. Fruits 12-13mm across, dark-red to brownish-red. Leaves whitish beneath, entire towards the tip but becoming deeply lobed to pinnate at the base, typically with two pairs of leaflets at the base and narrowing towards the tip.
The taxonomy of the former, much broader genus Sorbus is complicated and involves novel species that originated as stabilised hybrids from two other species. Bastard Service-tree is probably stabilised from hybrids between Common Whitebeam and Common Rowan, but it is unclear exactly how plants under this name in cultivation relate to naturally-growing populations.
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Swedish Service-tree Hedlundia hybrida
(Sorbus hybrida) Introduced from northern Europe. Occasionally planted but recorded just once in East Anglia, in West Suffolk. Flowers May to June, small, but carried in many-branched, flattened heads. Fruits 10-15mm across, orange-red with scattered pale freckles. Leaves whitish beneath, deeply lobed and becoming pinnate at the base and with a broadly rounded tip.
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Wild Service-tree Torminalis glaberrima
(Sorbus torminalis) Native in southern Britain and in the south of the East Anglian region, but also planted and only likely to be native in older, species-rich woodlands. Flowers May to June, a little larger and carried in more open heads than other Sorbus species in the region. Leaves green, the blade deeply lobed with distinctive, sharp-pointed lobes that get progressively larger towards the base.
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