Black poplar (Populus nigra), thought to be Britain's most endangered native timber tree (3), has a wide, rounded crown and dark grey fissured bark, with many swellings ('bosses') on the trunk (2). The deep green leaves are roughly triangular or oval in shape and become yellow in autumn (4). The flowers occur on three to five centimetres long catkins (2), and male and female flowers are produced on separate trees; male flowers have red anthers and female flowers have green stigmas(2). Old specimens often develop an obvious lean (5), and older branches are frequently pendulous (6).
This deciduous tree produces catkins in March and April, before the first leaves appear, and is pollinated by the wind (2). The fruits are green capsules that open up to reveal the very small seeds that have wispy hairs attached (4), which aid their dispersal in the wind (9). In order for this tree to regenerate, male and female trees must be fairly close together, and fertilised seeds must fall on bare soil that is still moist in June (5).
The timber, which is springy and light, is highly resistant to fire, and has been used for a variety of purposes, including floorboards, clogs and arrows that were found on the Elizabethan galleon, the Mary Rose(5).
The native subspecies of black poplar, Populus nigra betnifolia, is locally frequent in parts of lowland England and Wales, rarer in the north of England and Scotland, and rare in Ireland (6)(7), and also occurs in western Europe. At present the British population numbers just 2,000 to 3,000 trees (3). Elsewhere, black poplar is widely distributed but increasingly scarce throughout much of Europe reaching into central Asia and North Africa. It is generally absent from the far north of Europe (8).
The black poplar typically inhabits lowland floodplains (8) in river valleys (4) and needs open areas to allow germination(8). It also occurs in hedges and roadsides, and by ponds. Furthermore, it is sometimes planted in urban areas (6).
The preferred habitat of the black poplar has become very rare across Europe as floodplains have been modified and drained for agricultural purposes or succumbed to development pressures (10). Other threats include hybridisation with introduced poplars, which degrades the gene pool, competition with hybrids, and reductions in the groundwater table, which results in trees drying out and dying (8).
Part of the stamen (the male reproductive organ of a flower) that produces pollen. (See http://www.rbgkew.org.uk/ksheets/pdfs/flower.pdf for a fact sheet on flower structure)
A plant that sheds its leaves at the end of the growing season.
The beginning of growth, usually following a period of dormancy and in response to favourable conditions. For example, the sprouting of a seedling from a seed.
Cross-breeding with a different species.
To transfer pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
The receptive part of the female reproductive organ of a flower. Pollen germinates on the stigma. (See http://www.rbgkew.org.uk/ksheets/pdfs/flower.pdf for a fact sheet on flower structure).
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