Monday, 30 March 2009

Wood Spurge - the Gardenia of the woods? (*Euphorbia amygdaloides*)

The Euphorbias, alias the spurges, include some of the most statuesque of garden plants. And in the natural woodlands the wood spurge commonly strikes a dramatic pose. Its large clusters of yellowish flowers formed not of petals but yellowish bracts are eye catching. Each plant stands up to eighty cen-timetres high. Each red stem has a perennial drapery of drooping large thick, deep-green leaves which tend to be purple on the underside. The young shoots with their small, still growing leaves usually flop to one side. A thick white latex oozes out from any broken stem. This latex is extremely acrid in taste and can burn the skin. It is hardly surprising that one does not usually see any damage caused by predators. The plant is common throughout France, but in Britain it becomes rare north of a line from the Mersey to the Wash.
Here and there in most springs I see stands of the plants with the topmost drooping growth replaced with clumps of broader pale yellow/green leaves standing straight. The photo compares the abnormal on the left (plus one fly) with the usual form on the right. You might imagine that the yellow form was just an aberration, a variation, but then you notice that groups of flies are settling on them. I have also seen a small yellow slug eating a yellow leaf. Unfortunately when I bring the camera close enough to get a picture the flies tend to fly off.
But pick a deformed stem and immediately there is a powerful and delightful scent. In contrast the ordinary dull green and purple leaves smell musty and earthy. The odour of the deformed leaves re-minds me of gardenias. It is unexpected. One must suppose that the flies and slug are attracted to the smell and are devouring the exudations from the leaves which produce it. But what causes the smell? I remember the experience from long ago of a similarly strong scent emanating from a fungus disease ( a ‘rust’ disease) on creeping thistle. Indeed, examination of the leaves under the microscope show that each yellow leaf bears hundreds of minute red fungal pustules. These each exude an aromatic liq-uid. This it is a ‘rust’ known as Endophyllum euphorbiae-sylvaticae, rarely found in Britain. It only lives on the wood spurge and no other species of spurge. It has contrived to change the shoots of the spurge into yellow scented ‘flower’ forms to attract the flies which would most surely carry the spores of the fungus to new plants. I also wonder if any other animals would eat these soft, yellow, scented leaves?

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