Family Salicaceae
Populus

Six kinds of Poplar are commonly grown in this country, of which three are regarded as indigenous species. These are the Aspen, the Grey Poplar and the Black Poplar. Then, of common introduced species, we have the White Poplar, the Lombardy Poplar and the hybrid Black Italian Poplar.
The Poplars share their love of the Willows for moist places. Their growth is rapid, and their timber, consequently, is of little value, though its softness and lightness render it suitable for many uses, such as box-making and flooring. An additional point in favour of White Poplar for the latter purpose is its unreadiness to burn.
The Poplars and the Willows agree broadly in the construction of their flowers in catkins, but whereas the Poplars have broad leaves and drooping catkins, the Willows, with few exceptions, have long, slender leaves and erect catkins. The sexes are not only in distinct flowers, but on separate trees, and the males appear to be far more numerous than the females. In the popular sense there are no flowers, for there are neither sepals nor petals, each set of sexual organs being protected merely by a scale. The catkins usually appear before the leaves. As there is nothing to attract insects to the work, the Poplars have to rely upon the wind for conveying the pollen to the female trees.
The White Poplar, or Abele (Populus alba), is not so tall a tree as the Grey Poplar, generally not exceeding fifty feet in this country. Covered with smooth grey bark, its branches spread horizontally, and its lobed, maple-like leaves are hung on long, slender foot-stalks, which are flattened at the sides, so that when moved by the wind they flutter laterally. The leaves vary in shape. Those on long vigorous shoots and suckers are large, triangular in shape and deeply lobed. They are slightly hairy on the upper surface and covered with a dense snow-white felt on the under side. The leaf buds and young twigs are similarly covered. The leaves on the short shoots are oval, less deeply lobed and often not so densely hairy on the under surface.
The catkins, which appear in March and April, are cylindrical; those of the male trees are rarely, if ever, seen in Britain. The female catkins are about an inch long, the two yellow stigmas are slender, with slit tips, and the ovaries develop into slender egg-shaped capsules, each with its fringed scale.
In July when the seed capsules open, the surrounding vegetation and ground are thickly strewn with the long, white cotton filaments attached to the seeds.
The wood of this tree is softer and spongier than that of other Poplars. This species is said not to produce flowers in Scotland.
The Grey Poplar (Populus canescens), which is thought to be indigenous only in central and southern England, attains to eighty or ninety feet, with a girth of ten to twenty-four feet. Its life extends to about a century, but its wood is considered best between fifty and sixty years of age.
The leaves on the short shoots are shaped like those of the White Poplar, but their undersides are either coated with grey down or are quite smooth; those of the long shoots have their margins cut into angles and teeth. The female flowers mostly have four wedge-shaped purple stigmas, which are cleft into four at their extremities.
The Aspen (Populus tremula) does not attain either to so large a size or so moderate an age as the Grey Poplar. Its height, when full-grown, is from forty to eighty feet, and after fifty or sixty years its heart-wood begins to decay, and its destruction is then hastened by the attacks of such internal-feeding insects as the caterpillars of the Goat-moth and the Wood Leopard-moth.
The leaves on the branches are broadly egg-shaped, the waved margin cut into teeth with turned-in points. In one form (var. villosa) the leaves are covered beneath with silky or cottony hairs; in the other form (var. glabra) they are almost smooth. The leaves on the suckers are heart-shaped, with glandular teeth. The leaf-stalks are longer than those of its congeners, so that they are constantly on the flutter.
The catkins which are two or three inches long are similar to those of the White and Grey Poplars, but the scales have jagged edges.
It is indigenous in all the British Islands as far north as Orkney, but, though commonly found in copses on a moist, light soil, is more frequent as a planted tree in gardens and pleasure grounds. It is a characteristic tree of the plains throughout the Continent, but ascends to 1,600 feet in Yorkshire, and in the Bavarian Alps is found as high as 4,400 feet. It is not deep-rooted, and the root-branches run almost horizontal. Where accessible to cattle and deer, the foliage of the suckers is eagerly browsed by them.
The Black Poplar (Populus nigra) appears to be so called, not by reason of any blackness of leaf or bark, but because of the absence of any white or grey down on the underside of its leaves. Its bark is grey, and readily distinguished by the great swellings and nodosities that mar the symmetry of its trunk.
It is a tree of erect growth, fifty or sixty feet in height, with horizontal branches, and leaves that vary in shape from triangular to almost circular, and in width from an inch to four inches. They have rounded teeth on the margins, and in their young state the underside is silky.
The flowers in the catkins are not densely packed. Those of the male are two or three inches in length, and dark red in colour; their abundance before the tree has put out its leaves makes the male tree a conspicuous object. The female catkins are shorter and do not droop. When the roundish capsules burst in May or June to distribute their seeds, the white cotton with which the latter are invested gives prominence to the female tree.
The wood is chiefly used by the wood-turner; in Holland, where it is extensively cultivated, it provides the material for sabots.
The Black Poplar is indigenous in the eastern counties and in Wales. Some botanists regard the Lombardy Poplar as a variety of the Black Poplar, as apart from the very different habit of the tree – not by itself sufficient grounds for separation – there is little else to distinguish it.
The Lombardy Poplar (Populus italica) was for many years a tree of mysterious origin. It appeared in Italy about the middle of the eighteenth century, and was called Lombardy Poplar in consequence of its introduction thence by Lord Rochford in 1758. The original was a male tree, and as practically all of the vast number of Lombardy Poplars now existing have descended from cuttings or suckers of that tree, they are also males. The general supposition is that the original tree arose as a sport from the Black Poplar. A few females are known to exist, and these are probably the offspring of a later crossing.
Its glossy leaves are shaped like those of the Black Poplar, but its branches, instead of spreading, all grow straight upwards, so that the spire-shape of the tree is produced – a shape only found otherwise among coniferous trees, particularly in the Cypress, the Juniper and the Irish Yew.
It is its form, great height (80 to 100 feet), and rapidity of growth that have led to its wide use here as an ornamental tree. Its growth is extremely rapid, especially during its first twenty years, when it will attain a height of sixty feet or more, provided it be grown in good, moist (but not marshy) soil.
Its wood is, of course, of little value, and is chiefly used for making boxes and packing-cases, where its lightness, combined with toughness and cheapness, is an advantage.
The bark is rough and deeply furrowed; the furrows are spiral. Like the Black Poplar, it has smooth shoots, and the unopened buds are sticky.
The Black Italian Poplar (Populus serotina) appeared in the eighteenth century apparently as a result of the crossing of the Black Poplar with an American species (P. deltoidea).
The stem is free from the swellings and burrs of the Black Poplar and the spreading, ascending branches form a fan-like crown. The leaves are oval, about three inches broad, toothed and fringed. It comes into leaf much later than any other Poplar and is probably the commonest Poplar to be seen in the British Isles.
The Ontario or Balsam Poplar (Populus candicans) is of unknown origin. Usually known as the Balsam Poplar in this country it is frequently found as a planted tree. It is often confused with the American Balsam Poplar (P. tacamahaca), which is rarely seen in cultivation in England. The Ontario Poplar has broadly ovate leaves which are dark-green with few hairs on the upper surface and whitish on the lower surface. It produces many suckers.
The distinctive character of the tree is the fragrance of its young foliage, which scents the air on moist evenings, and makes it a desirable tree to plant near water.