+Laburnocytisus 'Adamii'
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 +Laburnocytisus 'Adamii' has flowers typical of both laburnum and broom
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| +Laburnocytisus ? |
+Laburnocytisus 'Adamii' (also known as Adam's laburnum or broom laburnum) is a horticultural curiosity; a small tree which is a graft-chimaera between two species, a laburnum, Laburnum anagyroides, and a broom, Chamaecytisus purpureus (syn. Cytisus purpureus), which bears some shoots typical of the one species, some of the other, and some which are a peculiar mixture of both "parents".
+Laburnocytisus 'Adamii' is a legume, a member of the pea family Faboideae (or Papilionaceae, formerly Leguminosae). The plus sign (+) indicates its unusual origin. The plant can also be described by the formula Chamaecytisus purpureus + Laburnum anagyroides. (It has also been known as +Laburnocytisus adamii, as if it were one species, but strictly speaking it is not one species but two.) Only one cultivar, 'Adamii', is known to have arisen from this graft.
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[edit] Appearance
Most of the tree's branches resemble the laburnum in their foliage, which has three leaflets (3-palmate) and 3–6 cm long, yet also with dense clusters of broom-like shoots, also with three leaflets, but only 1 cm long and a darker green. It flowers in late spring or early summer; some branches have long (20–30 cm) racemes of yellow laburnum flowers, while others produce dense clusters of purple broom flowers. Remarkably, most branches will also produce coppery-pink flowers on short (8–15 cm) racemes, which are midway between the two "parents"; the leaves on these shoots are also intermediate. In older specimens, the proportion of broom and mixed tissues tends to decline, and the laburnum to predominate. The tree grows to a height of 7 m (rarely 8 m) and is hardy to USDA plant hardiness zone 5 in northern Europe. It requires moderately fertile, moist but well-drained soil and should be grown in a sunny position to flower well.
[edit] Origin
The plant originated in the nursery of M. Adam near Paris in 1825, probably as an accident[1]; Chamaecytisus purpureus is normally a low-growing plant, and grafting it onto a straight trunk of a related species would be expected to create an attractive, semi-weeping standard.
In theory, other +Laburnocytisus could be developed in the same way but using different "parents"; a white-flowered broom might make a more attractive, if less striking, partner for the yellow laburnum.
[edit] Structure
A graft-chimaera is not a true hybrid but a mixture of cells, each with the genotype of one of its "parents"; it is a chimaera, created by grafting, in which the tissue of one plant grows within an outer envelope of the second plant. In the case of +Laburnocytisus 'Adamii', laburnum forms the core, surrounded by the broom.[2] Such plants are often called "graft hybrids", but as they are not true hybrids the use of this term is now discouraged.
[edit] Other graft-chimaeras
+Crataegomespilus is a graft-chimera between hawthorn (Crataegus) and medlar (Mespilus) which arose in a similar manner. There are two distinct cultivars that have arisen from this graft: +Crataegomespilus 'Dardarii' and +Crataegomespilus 'Jules d'Asnieres'.[3]
