Populus nigra subsp. betulifolia
Common names: Black poplar, downy black poplar
Irish name:
Latin name: Populus nigra subsp. betulifolia
Family: Salicaceae
Origin: Possibly native
Tree type: Deciduous broadleaf tree
How it looks
Shape, bark, twigs
Black poplars can grow to 30m tall. The bark of a mature black poplar is grey-brown, deeply fissured, burred, and rugged in texture. New shoots, known as epicormic growth, frequently emerge from the trunk. Its twigs are lumpy, a shiny orange-brown, and mostly hairless.
Buds
The tree's buds are sticky, smooth, and brown, with a greenish base, which are closely held to the twig while alternating up the stem.
Leaves
The leaves grow alternating along the stem and can be distinguished from other poplar species by their distinct diamond-shaped leaves. They also lack glands at the base of the leaf, do not emit a balsam odour, and feature a red leaf stem (petiole). These leaves measure 5 to 10 cm long, with very slight, bluntly toothed edges, a glossy bright green upper surface, and a paler underside.
Flowers
The black poplar is dioecious, meaning male and female flowers are found on separate trees. The flowers take the form of catkins and typically emerge in April. Male catkins are red and measure 3 to 5 centimetres in length, and are often referred to as "devil fingers." Female catkins are lime green and are pollinated by the wind.
Fruits
Once female catkins are fertilised, they enlarge and release numerous fluffy, cotton-like seeds that can be dispersed by wind or water. These seeds have evolved to repel water, allowing them to float and be carried over long distances by rivers. They remain viable for about two weeks and require specific conditions for successful germination, such as being deposited on wet soil. Flooding or drought during the germination phase can lead to seedling failure. Nonetheless, the black poplar has an additional survival strategy. Natural propagation can occur when tree fragments break off and take root, creating clones of the parent tree. In environments near riverbanks, the river's water can transport limbs hundreds of meters away. The tree can also send out suckers from its roots to generate new trees.
Similar species
Populus nigra subsp. betulifolia is similar in appearance to other poplar varieties like P. nigra ‘Italica and the hybrid black poplar, P. x canadensis. Notably, the leaves of P. nigra subsp. betulifolia have elongated tip similar to the silver birch, hence its subspecies name betulifolia (birch-leaved). Another distinguishing feature is its branches and twigs, which droop down and then ascend back up at the tips, differing from the generally upswept branches of the others. Identifying these differences can be challenging and often requires expertise for confirmation.
Another similar species is the white poplar, Populus alba. White poplars have rounded leaves compared to black poplars with more triangular/diamond-shaped leaves.
Where to find it
Populus nigra subsp betulifolia is rare in Ireland, being found mostly in the midlands, particularly within hedgerows in wet farmland near deep water-filled ditches. While native to Britain, Western Germany, and Northern France, its native status in Ireland remains unconfirmed. However, as one of Europe's most threatened tree species, the population found in Ireland is of international importance, especially those found in Lough Allen, where they are genetically distinct from all others found in Ireland and Britain.
The natural habitat of this subspecies is characterised by wet woodlands situated along lowland river valleys and floodplains. These trees thrive when they have ample space away from other trees and can bask in full sunlight.
Cultural importance
History
Whether native or introduced from Britain to landed estates during the eighteenth and nineteenth centuries, the Black Poplar appears to have little historical or cultural significance in Ireland. Indeed, historically, it seems that farmers and landowners tended to cut down female Black Poplars due to the great numbers of large cotton-like seeds they shed during the summer. However, one 150-year-old Black Poplar with a girth of seven metres from Spencer Harbour, County Leitrim gained such renown that has been entered into the national tree register as a champion specimen.
Black Poplar appears to have been of greater significance in British contexts. Evidence from archaeological excavations carried out in York demonstrate that it was used in the construction of a well during the Viking period (c. 866-1066 AD). In terms of weaponry, arrows made of black poplar were discovered within the wreck of sixteenth-century Tudor navy vessel, the Mary Rose. Up until the mid 1700s, its timber was used for various purposes, including fencing, house construction, footwear, weapons, domestic vessels and firewood.
Another source reveals that the early shoots of the black poplar were used for animal fodder, whilst a nineteenth-century account notes that its bark was used for making fishing net floats and for tanning leather. Its timber was especially valued in the construction of houses as it is fire-resistant, and for this reason it was often used for floorboards near fireplaces.
On account of its natural springiness and resistance to shock, black poplar was traditionally used to craft cartwheels and wagon bottoms. The flexible young shoots of coppiced black poplar were commonly used for bean sticks, clothes pegs and woven fruit baskets. Furthermore, as the wood of the black poplar has an affinity for absorbing paraffin, it was historically valuable for the production of matches. Other uses include the crafting of trays, bowls and clogs.
It has also been suggested that, due to their distinctive appearance, black poplars were often used to mark parish boundaries.
Art and Literature
The black poplar features in early Medieval English runic poetry, including the poem, ‘Under the Tree Called Beorc’, which speaks of the tree’s beauty. In addition, Fiona Cooper maintains that the trees referred to in William Cowper’s eighteenth-century poem, The Poplar Field, and Gerard Manley Hopkins’ nineteenth-century poem, The Binsey Poplars, are black poplars. Both works lament the felling of poplars and the loss of their virtues. The nineteenth-century artist John Constable also painted a black poplar in his famous work, The Hay Wain.
Value to wildlife
Black poplar is a valuable species for wildlife, with many specialist insects associated with it. It is an important food plant for the caterpillars of many moths, including the luna hornet, poplar hawk and figure of eight. Furthermore, its catkins serve as an early source of pollen and nectar, benefiting pollinators, while its seeds are a favoured food source for finches.
The black poplar is associated with riverside woodland. The extensive root system of the back poplar trees plays a crucial role in stabilising riverbanks and preventing soil erosion. This stability provides a supportive habitat for diverse wildlife along riverbanks and lakesides, including otters and kingfishers.
Threats
The female black popular has historically been disliked by landowners due to the vast amounts of snow-like seeds produced in late summer. In the UK especially, this is thought to be why so few female trees remain. In Ireland and Britain, the black poplar are so few and far between that they can rarely pollinate each other naturally. Instead, many cultivated poplar trees pollinate them, resulting in hybrids.
To learn more about threats to Irish trees, visit ‘Threats to Trees.'
Uses
Black poplar wood is yellow-white, fine textured, soft and said never to splinter. It can also be helpful in construction, having been used for thatching spars, rafters, poles, and rails. The branches of mature trees naturally grow with a curved shape, enabling their timber to be fashioned into arched supports for timber-framed buildings.
Beyond its applications in woodworking, black poplar had a place in traditional medicine. An ointment created from its buds was believed to be effective in treating conditions like bruises, inflammation, and gout. In modern herbalist practices, this species helps address ailments such as arthritis, bronchitis, haemorrhoids, and rheumatic diseases.
References
Cambridgeshire & Peterborough Biological Records Centre. 2006 Black Poplars (Populus nigra betulifolia) in Cambridgeshire. A survey co-ordinated by Cambridgeshire & Peterborough Biological Records Centre. Microsoft Word - Black Poplar_report_final.doc (cperc.org.uk)
Cooper, F. 2006. The Black Poplar, Oxford: Windgather Press
Cooper, F.M.P., Jones, M., Watkins, C. and Wilson, Z. A. 2002. Geographic distribution and Genetic Diversity of Black Poplar. R&D Technical Report W1-022/TR, Environment Agency, Bristol, 1-54.
Hobson, D.D. 1993. Populus nigra L. in Ireland - an indigenous species? Irish Naturalists Journal 25, 244-247.
Horn, P. C. 2021. The Black Poplar tree in Anglo-Saxon England, The English Companions Website. The Black Poplar tree in Anglo-Saxon England – Tha Engliscan Gesithas (tha-engliscan-gesithas.org.uk)
MacSweeney, E. 2023. Gender bias seems behind vulnerable Black Poplar’s imbalance - but at least there’s cloning, The Irish Times. Gender bias seems behind vulnerable Black Poplar’s imbalance - but at least there’s cloning – The Irish Times
Meikle, R. D., & Gordon, V. (2001). Willows and poplars of Great Britain and Ireland (Repr). Botanical Society of the British Isles.
Stroh, P. A., Humphrey, T. A., Burkmar, R. J., Pescott, O. L., Roy, D. B., & Walker, K. J. 2023. BSBI Online Plant Atlas 2020. https://plantatlas2020.org/atlas
Tree Council of Ireland. 2024. Native Irish Trees. Tree Council of Ireland. https://www.treecouncil.ie/native-irish-trees
Woodland Trust. 2024. A-Z of British trees. Woodland Trust. https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/