Sorbus intermedia Seeds | Swedish Whitebeam
LATIN NAME: Sorbus intermedia
COMMON NAME: Swedish Whitebeam, Intermediate Whitebeam
Plant Profile
The leaf is seven to twelve centimetres long, deeply cut into pointed lobes toward the base and less so toward the tip, dark green and slightly glossy above, and covered beneath with a grey felt of dense hairs. That white underside is the family trait behind the name whitebeam, and it shows whenever the wind lifts a shoot. In autumn the foliage turns yellow and dull bronze, and the tree holds it late. The bark is smooth and grey, becoming shallowly fissured on old trunks, and the buds are sticky in spring.
Flat-topped clusters of white flowers open in late spring, and they carry the sweetish, faintly animal smell that runs through the genus, a note produced largely by trimethylamine rather than by a conventional floral oil. Beetles, hoverflies and bees work the clusters, and the flowers set fruit reliably because the seed does not depend on a partner. The pomes that follow are orange-red, about the size of a pea, borne in loose bunches that stay on the tree well into winter.
The rose family moves sugars in a way most plants do not: sorbitol, a sugar alcohol, is loaded into the phloem, and it was first isolated from a Sorbus species. The enzymes that build and unload it, aldose reductase and sorbitol dehydrogenase, have been studied across fruit trees because their activity tracks drought and cold response, and the Sorbus species are a natural comparison point for the apple, pear and cherry lines that breeders care about. The whitebeam also stores sorbitol in its pomes, which is part of their sweetness.
Science & Biotechnology
Apomixis is a long-standing goal of plant genetics, since a crop that bred true from seed would fix a hybrid permanently, and apomictic Sorbus species have served as study material for the embryo-sac development behind it. Related work on the genus deals with the saponins and with parasorbic acid, the lactone that gives rowan-group pomes their bitter, astringent edge. Nursery selection has concentrated on narrow-crowned forms for street planting, where a tight head resists wind damage.
Uses & Benefits
Swedish whitebeam earns its keep in the open, exposed places where tidier ornamental trees fail. It tolerates lime in the soil as well as the acid ground its rowan parent prefers, takes salt spray on the coast, and holds a rounded crown without staking. Cities across northern Europe use it as an avenue tree and in car parks, and because the fruit hangs in loose clusters rather than in a heavy crop, the pavement stays cleaner than under many fruiting trees. For the kitchen the pomes are too bitter and mealy to eat raw, but they soften after frost and make a sharp jelly by the method used for rowan. The pale, close-grained wood takes a fine polish and was once worked into tool handles and small turnery, and the winter fruit feeds thrushes and waxwings when little else is left.
Growing from Seed
The Swedish whitebeam sets fertile fruit, and yet its offspring are not a mixture of two parents. The species is an apomict: seed forms without fertilisation of the egg, so every seedling is effectively a cutting of the mother tree, and the northern population is made of near-identical lines that keep a particular leaf shape wherever they grow. That is remarkable enough on its own, and it explains why the tree has been so useful in towns, since a street tree that comes true from a handful of seed is a gift to a nursery.
The species arose as a hybrid between the whitebeam, with its simple lobed leaves, and the rowan, with its pinnate ones. The result sits between them, and that mixture is where the name intermedia comes from. It is also, conveniently, a better street tree than either parent on windy, salt-laden coasts.
Scoop the seeds out of ripe pomes, rinse away the pulp, and sow them about a centimetre deep in a mix of two parts loamy topsoil, one part composted bark and one part grit. A cold, damp winter rest follows naturally in an outdoor frame, and thinning is rarely needed because so much of the seed is apomictic and the plants come up uniform. Space nursery rows forty centimetres apart and final plantings two to three metres apart for an avenue.
Water a young whitebeam well for the first two seasons and then leave it alone; it resents fussing and quickly builds a deep root. Prune in winter, taking out the lowest branches gradually until the clear stem stands at about two metres, then stop, because the species makes a broad natural head and dislikes being clipped into shape. Aphids on the young shoots are the common complaint, and bullfinches strip the flower buds in hard winters, which costs you the fruit for that season but does the tree no lasting damage. Fireblight is the disease to watch in warm, wet summers, and any shoot that blackens and hooks should be cut out well below the damage.
Our Take
If you want a tree that will grow without ceremony on a windy, chalky or coastal site, this one asks for nothing beyond firm planting and a season of watering. Its whitebeam parent, grown for the silver underside of the leaf, is covered in Sorbus aria, and the larger service tree with its edible brown pomes is described in Sorbus domestica. Gardeners further west who want the rowan side of the family will find the mountain-ash notes useful in Sorbus sitchensis. Any of the three sits happily beside a whitebeam in an exposed planting.
Related Reading
Gardeners who grow Swedish Whitebeam often pair it with these related subjects: