Laburnum alpinum
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Jonny & Sara Shaw
Credits
Owen Johnson (2024)
Recommended citation
Johnson, O. (2024), 'Laburnum alpinum' from the website Trees and Shrubs Online (treesandshrubsonline.
Genus
Common Names
- Alpine Laburnum
- Scottish Laburnum
- Alpine Goldenchain
Synonyms
- Cytisus alpinus Mill.
Infraspecifics
Other taxa in genus
Tree to 14 m tall, usually with a short trunk and ascending main branches. Bark grey to brownish. Young twigs green, glabrescent. Leaflets narrowly ovate to broadly lanceolate, 5–10 cm long, deep green, with just a few silky hairs beneath. Raceme with a glabrous or finely pubescent rachis, 20–30 cm long; flowers with glabrous or finely pubescent pedicels. Flowering around June (but into July in cool climates). The upper seam (suture) of the legume is distinctly winged to form a sharp edge. (Bean 1981).
Distribution Albania Austria Bosnia and Herzegovina Croatia Czechia In the south France In the Alps Greece In northern mountains Italy In the Alps and northern Apennines North Macedonia Serbia Slovenia Switzerland
Habitat Mountain forests and open but not dry places; not confined to limestone.
USDA Hardiness Zone 5-9
RHS Hardiness Rating H6
Conservation status Least concern (LC)
The name Alpine Laburnum aptly indicates the preference of Laburnum alpinum for slightly cooler and wetter conditions than its fellow European endemic the Common Laburnum, L. anagyroides. The species is not however confined to the Alps, and its native distribution extends along the northern Appenines in Italy, the western Carpathians in Czechia, and across the mountains of the Balkan Peninsula as far as northern Greece (Royal Botanic Gardens, Kew 2024; Bean 1981). The more parochial ‘Scots Laburnum’ reflects how well adapted the tree is to comparable microclimates much further north; like another characteristically Alpine tree, the Sycamore (Acer pseudoplatanus), L. alpinum is one of the most valued trees in extreme maritime exposure, as in gardens in the Shetland Islands (Tree Register 2024), and massive, old-looking trees can be encountered in some quite remote corners of the Scottish Highlands.
This is a tree of often slightly larger stature than Laburnum anagyroides, with a slightly greyer bark, slightly bigger (but not broader), deeper-green leaves and longer racemes of flowers which open a fortnight or two later; it is less hairy, and one more precise differentiating feature is the sharp-edged wing along the upper side of the seed-pod. The longer racemes, which consequently hang more perfectly straight, perhaps make for a more graceful flowering display, but some of the hybrids which have arisen between the two species are claimed to bear even longer flower-heads, more densely packed with blooms. These hybrids also blur the mostly subtly differences between their parents: for all except the most determined observers, any laburnum will simply be a laburnum. A few geographical variations have been observed within the wild populations of L. alpinum; var. pilosum Wettst. describes a more pubescent form, common in northern Italy, and f. microstachys (Wettst.) Koehne describes trees with shorter racemes, from the eastern end of the species’ range (Bean 1981). Very few modern references recognise these variants.
'Autumnale'
Synonyms / alternative names
Laburnum alpinum 'Biflorum'
Laburnum alpinum var. autumnale was described in the first edition of Trees and Shrubs Hardy in the British Isles (Bean 1914; Royal Botanic Gardens Kew 2024) as one of several laburnums selected to flower throughout summer or again in autumn. The nurseries supplying these selections were unlikely to be particular about which species they best belonged to, and a L. anagyroides var. autumnale had already been described from Prussia by K. Koch in 1859 (Royal Botanic Gardens Kew 2024).
The planting list for an arboretum established in 1935 in Thorpe’s Wood, a part of Alexandra Park in Hastings, UK, incuded two ‘Laburnum autumnale’ (most likely supplied by Hilliers Nurseries). These survived until the 1980s, when as a teenage aspiring dendrologist the author felt that they had foliage characteristics of L. alpinum. Possibly because of their age, they no longer showed any signs of autumn flowering. There are no other records to indicate the selection’s continued survival anywhere.
'Grandiflorum'
Represented in 2023 by a small but old tree at the Royal Botanic Gardens, Kew, which is perhaps too shaded to be at its best as a flowering plant, and which lacks accession details. This was presumably an old selection for the large size of its individual flowers.
'Latest and Longest'
Described in older editions of Trees and Shrubs Hardy in the British Isles as ‘still one of the best laburnums’ (Bean 1981), ‘Latest and Longest’ has also been grown in the United States (Jacobson 1996). Presumably, its sale name aptly described the floral display.
'Newryensis'
A robust, late-flowering clone selected at the Daisy Hill Nursery, Newry, Northern Ireland. One of the stock trees still grew here in 1997, as did one purchased from Daisy Hill in 1930 at the National Botanic Gardens of Ireland at Glasnevin, Dublin. There is also a record of a purchase in 1915 at the High Beeches, Sussex, England (Nelson 2000).
'Pendulum'
Weeping forms have been named for both Laburnum species. J.C. Loudon (Loudon 1838) first described a variant of L. alpinum with weeping branches from Loddiges’ London nursery, but nboted thats its foliage characters were intermediate between the species. He considered it more vigorous than L. anagyroides f. pendulum. In 2024, five specialist nurseries in the UK offered a L. alpinum ‘Pendulum’ (Royal Horticultural Society 2024), though it might be naive to assume that these offerings are genetically identical (or even necessarily belong within L. alpinum). One clone weeps strictly from a high graft; Arthur Lee Jacobson (Jacobson 1996) observed that similar trees in the north-western United States were shy-flowering. At the Jodrell Bank Arboretum, Cheshire, UK, in 2004, a weeping laburnum grafted at the base had grown gracefully to five metres, and its foliage features suggested L. alpinum (pers. obs.); this tree has since been lost.
'Pyramidale'
A fastigiate selection (Edwards & Marshall 2019), whose latinate name implies that it was registered before 1959. It was still offered in 2024 by Yamina Rare Plants in Australia (Teese 2024).
var. pilosum (Wettst.) Koehne
This minor variant is briefly discussed in the main text for Laburnum alpinum.