Populus nigra

Three subspecies are established and some botanists distinguish a fourth:[1][2]

• P. n. subsp. nigra. Central and eastern Europe. Leaves and shoots glabrous (hairless); bark grey-brown, thick and furrowed.

Burrs and normal bark on a black poplar tree (subspecies betulifolia) in Ayrshire, Scotland.

• P. n. subsp. betulifolia (Pursh) W.Wettst. North-west Europe (France, Great Britain, Ireland). Leaf veins and shoots finely downy; bark grey-brown, thick and furrowed, often with heavy burrs, trunk usually heavily leaning.
• P. n. subsp. caudina (Ten.) Bugała. Mediterranean region, also southwest Asia if var. afghanica not distinguished.
• P. n. var. afghanica Aitch. & Hemsl. (syn. P. n. var. thevestina (Dode) Bean). Southwest Asia; treated as a cultivar of P. nigra by many botanists,[5] and as a distinct species P. afghanica by others;[6] bark smooth, nearly white; leaves and shoots as subsp. caudina (see also cultivars, below).

The subspecies P. n. betulifolia is one of the rarest trees in Great Britain and Ireland,[7][8] with only about 7,000 trees known, of which only about 600 have been confirmed as female.[9]

Several cultivars have also been selected, these being propagated readily by cuttings:

• 'Italica' is the true Lombardy poplar, selected in Lombardy, northern Italy, in the 17th century. The growth is fastigiate (having the branches more or less parallel to the main stem), with a very narrow crown. Coming from the Mediterranean region, it is adapted to hot, dry summers and grows poorly in humid conditions, being short-lived due to fungal diseases. It is a male clone.[10] As a widely selected species chosen by golf architects in the 1960s, it soon became apparent that the poplar's very invasive roots destroyed land drainage systems. Decades later, the same courses were removing poplar stands wholesale. Around 40 to 50 years, this short-lived variety starts shedding branches and is very likely to be blown over in high winds, each successive tree lost exposing neighbouring trees, creating a domino effect.

A fastigiate black poplar cultivar of the Plantierensis group, in Hungary

• Plantierensis group clones are derived by crossing 'Italica' with P. nigra ssp. betulifolia at the Plantières Nursery near Metz in France in 1884; they are similar to 'Italica' (and often mistaken for it), but with a slightly broader crown, and better adapted to the cool, humid climate of northwest Europe, where the true Lombardy poplar does not grow well. Both male and female clones are grown. This is the tree most commonly grown in Great Britain and Ireland as Lombardy poplar.[10]
• 'Manchester' is a cultivar of P. nigra subsp. betulifolia widely planted in northwest England. It is a male clone, and currently seriously threatened by poplar scab disease.[11][12]
• 'Gigantea' is another fastigiate clone, of unknown origin, with a rather broader, more vigorous crown than 'Italica'. It is a female clone.[10]
• 'Afghanica' (syn. 'Thevestina'): most, if not all, specimens are of a single clone, and many botanists therefore treat it as a cultivar rather than a botanical variety. It is fastigiate, similar to 'Italica', but with a striking whitish bark; it also differs from 'Italica' in being a female clone. This is the common fastigiate poplar in southwest Asia and southeast Europe (the Balkans), where it was introduced during the Ottoman Empire period.[10]