Populus alba
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.