Plant 204

Sorbus torminalis (L.) Crantz (Rosaceae)


Wild service-tree

Wild service-tree is native to Europe. The strong hold of its distribution is southern Britain through central Europe into Poland and then southeast into the Balkans, northern Anatolia and Caucasus. There are scattered populations in the Iberian Peninsula and northwest Africa. This tall (to 25 m), deciduous tree has distinctive, simple leaves, white flowers arranged in flattened heads and small, spherical, spotted brown, apple-like fruits.

Wild service-tree is a lowland, light-demanding species that tolerates a wide range of soil conditions, although in Britain it is mainly found on clay and basic soils. In the British landscape it is a relatively rare tree of ancient woodland sites. Sorbus torminalis occurs at low density across its range and is regarded as of little overall conservation concern.

As might be expected from an insect-pollinated, self-incompatible species with animal-dispersed fruits, Sorbus torminalis is genetically diverse, showing extensive pollen and seed movement within and among populations, despite the wide separation of individual trees. Hot summers, which rarely occur in Britain, are necessary for wild service-tree seeds to mature. Consequently, at its northern and western limits, Sorbus torminalis propagates mainly though vegetative means such as suckers; there is lower genetic diversity in these areas than at the centre of its range.

In Britain, one traditional name for the fruits is chequers, which are edible but, like medlars, must be overripe to eliminate their astringency. Before the introduction of hops, wild service-tree fruits were used to flavour beer. The species epithet, torminalis, refers to another of the fruit's past uses; as a colic cure. Traditionally, wild service-tree wood has been used where tough, dense, fine-grained timbers are essential, for example, in gear cogs and shafts, and musical instruments. Today, it is used primarily in decorative veneers.

Sorbus torminalis is a diploid species (it has two complete sets of chromosomes) and has complex relationships with other members of the genus. For example, it has been implicated in the origin of tetraploid hybrid species (which have four sets of chromosomes) such as Sorbus intermedia and Sorbus latifolia. Furthermore, it is the female parent of the triploid hybrid species Sorbus bristoliensis, a British endemic found only in the Avon Gorge, Bristol. The male parent of Sorbus bristoliensis is Sorbus eminens, which is another British endemic species; both species are apomictic, that is they produce seed from female tissue only, fertilisation by male cells is unnecessary to produce a viable seed.

Further reading

Pellicer J et al. 2012. Cytotype diversity in the Sorbus complex (Rosaceae) in Britain: sorting out the puzzle. Annals of Botany 110: 1185-1193.

Rich T et al. 2010. Whitebeams, rowans and service trees of Britain and Ireland. Botanical Society of the British Isles.

Roper P 1993. The distribution of the wild service tree Sorbus torminalis (L.) Crantz, in the British Isles. Watsonia 19: 209-229.

Stephen Harris