+Laburnocytisus 'Adamii'

Taxobox | name = +"Laburnocytisus"


image_caption = +"Laburnocytisus" 'Adamii' has flowers typical of both laburnum and broom
regnum = Plantae
divisio = Magnoliophyta
classis = Magnoliopsida
ordo = Fabales
familia = Fabaceae
subfamilia = Faboideae or Papilionaceae
tribus = Genisteae
binomial = +"Laburnocytisus"
binomial_authority = ?

+"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.

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.

Origin

The plant originated in the nursery of M. Adam near Paris in 1825, probably as an accident; [ "Hillier's Manual of Trees & Shrubs" 5th Edition (1984) 164.] "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.

tructure

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. [ "Hillier's Manual of Trees & Shrubs" 5th Edition (1984) 164.] Such plants are often called "graft hybrids", but as they are not true hybrids the use of this term is now discouraged.

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'. [ "RHS Plant Finder 2006–2007" 20th Edition (2006) 202.]

References