18-June Willows, Poplars & Rare Giants

The closely related cricket bat willow S. alba coerulea has leaves that are blue-grey in colour, giving the whole tree a ‘bluish’ look. This is one of the fastest growing trees in Britain and can often be seen at the edges of fields, especially in Essex.

The goat, or pussy, willow S. caprea is everywhere there is waste ground as it is such a good coloniser. It has a broadly elliptical leaf with prominent veins and a leaf tip that is decidedly bent over.

The crack willow S. fragilis and osier S. viminalis both have long, narrow, pointed leaves. This month the undersides of osier leaves are both downy and silvery, whereas those of the crack willow are neither. The leaves of bay willows S. pentandra are strongly aromatic. The leaf of the almond-leaved willow S. triandra is far more almond-shaped than the others. The eared willow S. aurita is one of the easiest to identify because of its small leafy growths or ‘ears’ at the base of its petioles. The purple willow, which is popular with gardeners, has gracefully arching purple shoots. It can be checked by scraping slightly young shoots: the tissue below the surface is a surprising bright yellow. The violet willow S. daphnoides also has purple shoots, but they are also covered with a white bloom. The shapes alone of weeping and contorted willows make them easier than the others to identify.

Hybrids are generally much harder to separate as they have so many mixed characters. More unusual willows worth seeking out in gardens are the silver willow S. alba ‘Argentea’, which has more silvery leaves than most, and the coral-bark willow S. alba ‘Britzensis’, which has an attractive pink bark. The tiny, unobstrusive wild creeping willow S. repens can still be found in Epping Forest.

Different poplars are usually another headache to tell apart. Once again, it is slightly easier when their leaves are fully developed. Poplars beside water are usually grey, black or hybrid black. The base of the leaf in a black poplar Populus nigra is distinctly straight, forming a distinct spade shape. In a hybrid black poplar P x Canadensis it is weakly heart-shaped.

The veins on the leaves of both trees also differ. The veins on black poplars are more extensive and more clearly branched than those of the hybrid. Grey poplars P. canescens are often confused with white poplars P. alba. The undersides of grey poplar leaves tend to be grey as compared to the felted white colour of white poplar leaves. The leaves of aspens P. tremula are much more oval than the rest and also have a wavy outline.

If the smell of western balsam poplars P. trichocarpa is not enough to recognise them by then their leaves are distinctly arrowhead-shaped.

Similarly, Lombardy poplars P. nigra ‘Italica’ are instantly recognisable from their tall, thin silhouette, but their leaves are also recognisable as they are diamond-shape. Hybrids once again are a much harder proposition. Other rarer, foreign poplars are to be found in park collections. Worth seeking out is the Berlin poplar P x berolinensis (Cannizaro Park), P. simonii (Acton Park) and the Chinese necklace poplar P x lasiocarpa (Battersea park).

Other rare trees include some Eucalyptus spp. e.g. E. globulus which has exceptionally blue leaves and E. leucoxylon which has attractive, shiny, red flowers. Quercus rubra aurea, which can be found at Wisley, is an unusual oak with bright yellow leaves.

Cornus kousa with their eye-catching flowers and fruits and their relatives can also be found there. One distinctive tree in gardens across London at this time is the Mount Etna broom Genista aetnensis which may now be covered head to toe in bright yellow flowers. Although sometimes looking like a shrub, it can grow up to six metres in height. In the wild it is found high on the volcanic slopes of Mount Etna. June 18th is traditionally the first day of high summer, yet service trees Sorbus torminalis may already be showing the first hints of some autumn colour.