There are three species of Poplar that are common in Britain and several groups of hybrid varieties. Aspen, White Poplar and Grey Poplar are common species. Lombardy Poplar and Hybrid Black Poplars are the most common of the hybrid varieties. The Aspen is described elsewhere. White Poplar, Grey Poplar, Lombardy Poplar and Hybrid Black Poplars are described below. The Black Poplar, not described here, is rare in most parts of Britain but is common in the Vale of Aylesbury and in Manchester.
Poplars are wind pollinated and have flowers that are on catkins. Wind carries the pollen from male flowers to female flowers. Poplars have male flowers on one tree and female flowers on another tree. Technically they are called ‘dioecious’ from the Greek meaning ‘2 households’. This is only really apparent in spring when the catkins are present. Female and male catkins are different. When first produced they may look alike but male catkins soon drop off after releasing pollen, whereas female catkins turn green when fertilised and then later release white seeds which litter the floor like cotton.
The White Poplar (Populus alba) is native to central and southern Europe and central and southern Asia, was probably introduced to Britain but now grows naturally and has been planted in many gardens and parks. It does not grow as tall as the hybrid Grey Poplar with which it can be confused. The shoots, buds and underside of its leaves are covered in white hairs. In summer it is strikingly white in appearance. The Grey Poplar leaves can look white underneath in spring but become grey in summer. Leaves are variable in shape with those on strong-growing shoots being Maple-like.
The Grey Poplar (Populus canescens) is a natural hybrid between the White Poplar and the Aspen. It may have been introduced. It has a wide distribution in Europe and Western Asia. It is common throughout Britain. It is easily confused with the White Poplar but it grows faster and becomes a larger tree. Because the tree is a hybrid it may show aspects of both parents.
The Lombardy Poplar (Populus nigra ‘Italica’) is a form of Black Poplar that probably came originally from Northern Italy in the 18th century but has since been planted throughout the world as an ornamental tree. It is a male tree with red catkins in spring and can reach a height of more than 30m. The leaves are diamond-shaped and are hairless. The branches grow almost vertically to give it its characteristic shape.
Hybrid Black Poplars (Populus x euramericana) arise when the European Black Poplar is crossed with the American Eastern Cottonwood. Some hybrids are natural but many are artificial. Hybrid Black Poplars are common, some grown for timber but many in new towns because they grow rapidly. They are generally known by their ‘cultivated variety’ name such as ‘Robusta’, ‘Regenerata’, ‘Serotina’, ‘Eugenei’ etc.
White Poplar leaf shape is variable. The normal shape is like this. On strongly growing shoots the leaf shape is palmate. The underside is covered in white hairs and stays like this all summer.
The Grey Poplar leaf shape is a cross between the Aspen and the White Poplar. Some leaves in April can be very white underneath and can easily be mistaken for those of the White Poplar.
Lombardy Poplar leaves are diamond-shaped.
Leaf of the Hybrid Black Poplar ‘Robusta’ in June. This is one of the earliest poplars to come into leaf, in late April.
White Poplar female catkin in March before the leaves.
Grey Poplar female catkin in March.
Lombardy Poplar male catkin in March, before the leaves.
Male catkins of the Hybrid Black Poplar clone ‘Robusta’ in early March.