Populus × canescens

Populus × canescens, the grey poplar, is a hybrid between Populus alba (white poplar) and Populus tremula (common aspen). It is intermediate between its parents, with a thin grey downy coating on the leaves, which are also much less deeply lobed than the leaves of P. albus. It is a very vigorous tree with marked hybrid vigour, reaching 40 m tall and with a trunk diameter over 1.5 m – much larger than either of its parents. Most trees in cultivation are male, but female trees occur naturally and some of these are also propagated. In 1789 William Aiton described the grey poplar as a variety of Populus alba, P. alba var. canescens. In 1804, James Edward Smith raised it to a full species, Populus canescens. He described differences between the leaves of the two taxa: P. alba has lobed leaves with snow-white ('niveus') undersides, whereas P. canescens has wavy-edged leaves with hoary ('incanus') undersides. Later authors sometimes noted the possibility that the grey poplar was a hybrid. It is now considered to be a hybrid between Populus alba and Populus tremula, so the scientific name is written with the hybrid symbol.