POPLAR (Populus), the name of a small group of catkin bearing trees belonging to the family Salicaceae, which includes the willows. The catkins of the poplars differ from those of willows in the presence of a rudimentary perianth; the male flowers contain from 4 to 8o stamens; the fertile bear a one celled ovary, surmounted by the deeply cleft stigmas; the two valved capsule contains several seeds, each furnished with a long tuft of silky or cotton-like hairs. The leaves are generally either deltoid or ovate in shape, often heart-shaped at the base, and frequently with slender petioles vertically flattened. Many of the species attain a large size, and all are of very rapid growth. The poplars are almost entirely confined to the north temperate zone, but a few approach or even pass its northern limit, and they are widely distributed within that area; they show, like the wil lows, a partiality for moist ground and often line the river-sides in otherwise treeless districts. There are about 3o species, but the number cannot be very accurately defined, as there are many regional varieties, and also widely diffused hybrids of uncertain origin. All yield a soft, easily-worked timber. Many of the species are used for paper-making.
Of the European kinds one of the most important is the white poplar or abele, P. alba, a tree of large size, with rounded spread ing head and curved branches, which, like the trunk, are covered with a greyish white bark, becoming much furrowed on old stems. The leaves are ovate or nearly round, but with deeply waved, more or less lobed and indented margins and heart-shaped base; the upper side is dark green, but the lower surface is clothed with a dense white down, which likewise covers the young shoots— giving, with the bark, a hoary aspect to the whole tree. A nearly related form, which may be regarded either as a sub-species, canescens, or as a hybrid with the aspen (P. alba x tremula), the grey poplar of the nurseryman, is distinguished from the true abele by its smaller, less deeply cut leaves, which are grey on the upper side, but not so hoary beneath as those of P. alba.
Both trees occasionally attain a height of go ft. or more. The wood is very white, and, from its soft and even grain, is employed by turners and toy-makers; it is also serviceable for the con struction of packing cases, etc. The white poplar is an ornamental tree, from its graceful growth and its dense hoary foliage ; it has, however, the disadvantage of throwing up numerous suckers for some yards around the trunk.
P. nigra, the black poplar, is a tree of large growth, sometimes Ioo ft. high, with dark, deeply-furrowed bark on the trunk, and ash-coloured branches; the smooth deltoid leaves, serrated regu larly on the margin, are of the deep green tint which has given name to the tree; the petioles, slightly compressed, are only about half the length of the leaves. The black poplar is common in cen tral and southern Europe and in some of the adjacent parts of Asia, but, though abundantly planted in Great Britain, is not there indigenous. The wood is of a yellowish tint.
A closely related form is the well-known Lombardy poplar, P. fastigiata, remarkable for its tall, cypress-like shape, caused by the nearly vertical growth of the branches. Probably a variety of the black poplar, its native land appears to have been Persia or some neighbouring country; it was unknown in Italy in the days of Pliny, while from remote times it has been an inhabitant of Kashmir, the Punjab, and Persia, where it is often planted along roadsides for shade ; it was probably brought from these countries to southern Europe, and derives its popular name from its abund ance along the rivers of Lombardy, where it is said now to spring up naturally from seed, like the indigenous black poplar. It was introduced into Great Britain soon after 175o, if not earlier. The Lombardy poplar is valuable chiefly as an ornamental tree; its tall, erect growth renders it useful to the landscape-gardener as a relief to the rounded forms of other trees, or in contrast to the horizontal lines of the lake or river-bank. Its growth is extremely rapid and it often attains a height of too feet.