Our gardens are filled with hybrids but they are usually all produced by combining the genes of the two different parents. There is one notable exception to this*; Adam’s laburnum which is a hybrid of a laburnum and a broom. But this hybrid was not created by taking the pollen of one plant and putting it on the stigma of another to make a new plant that combined the genes of both in one plant. This is a graft hybrid and is a combination of both plants in such as way that the plant has pure laburnum cells and pure broom cells.
It was created by M. Adam at his nursery near Paris in 1825 and it was an accident. It is thought that he was trying to graft a pink broom (Cytisus purpureus) onto Laburnum anagyroides stocks to create a standard plant with weeping pink broom on top – rather like a standard rose or that awful weeping ‘Kilmarnock’ willow. One plant went wrong and a bud of the laburnum grew through the skin of a broom stem and the resultant plant is a chimera with an inner core of laburnum, covered in a layer of broom cells.
So what you get is basically a laburnum but with a thin skin of broom, rather like a hand in a glove, with the broom being the glove. The plant looks and grows like a laburnum but the flowers are yellow, overlaid with pink broom cells so the flowers are a curious, and not unpleasant, peachy pink colour.
But just as your gardening gloves can wear through, so sometimes the laburnum breaks through the broom cells and you get clusters of yellow, laburnum flowers. Less frequently the broom cells bunch up and you get a cluster of upright, broom flowers and congested broom leaves and twigs on the branches too – all very odd.
The full name of the plant is +Laburnocytisus ‘Adamii’. The ‘+’ is to denote that it is a graft hybrid and not a x Laburnocytisus which would denote an ‘ordinary’ hybrid between two genera.
Of course, such an extraordinary plant is not ‘mad’ enough for some catalogues so they cheat and illustrate it with the photo below, and others that owe their origin not with Mr Adam but with Photoshop. It is despicable and they should be stopped from trading. This one is from the Bakker catalogue but there are lots of others – you know who you are.
Anyway, it is a slightly unsatisfactory plant and never really looks that good. It is a curiosity and worth growing for that reason but don’t expect the sort of nonsense you see in the ‘fake photos’. Give it a sheltered spot and rich, well drained soil in full sun for best results but bear in mind that laburnums are not long lived at the best of times. Seeds will produce ordinary laburnums of course.
* There is also a medlar graft hybrid.