Populus tremula (*)
Populus tremula L.
* Species Plantarum 2:1034. 1753
Populus tremula (Aspen, or Common Aspen or Eurasian Aspen to distinguish it from related species) is a species of poplar native to cool temperate regions of Europe and Asia, from the British Isles  east to Kamchatka, north to inside the Arctic Circle in Scandinavia and northern Russia, and south to central Spain, Turkey, the Tian Shan, North Korea, and northern Japan. It also occurs at one site in northwest Africa in Algeria. In the south of its range, it occurs at high altitudes in mountains.
It is a medium-sized deciduous tree growing to 10–25 m tall, with a trunk up to 1 m diameter. The bark is pale greenish-grey and smooth on young trees with dark grey diamond-shaped lenticels, becoming dark grey and fissured on older trees. The adult leaves, produced on branches of mature trees, are nearly round, slightly wider than long, 2–8 cm diameter, with a coarsely toothed margin and a laterally flattened petiole 4–8 cm long. The flat petiole allows them to tremble in even slight breezes, and is the source of its scientific name. The leaves on seedlings and fast-growing stems of root sprouts are very different, heart-shaped to nearly triangular, and often much larger, up to 20 cm long; their petiole is also less flattened. The flowers are wind-pollinated catkins produced in early spring before the new leaves appear; they are dioecious, with male and female catkins on different trees. The male catkins are patterned green and brown, 5–10 cm long when shedding pollen; the female catkins are green, 2–4 cm long at pollination, maturing in early summer to bear 10–20 capsules each containing numerous tiny seeds embedded in downy fluff. The fluff assists wind dispersal of the seeds when the capsules split open at maturity.
It can be distinguished from the closely related North American Populus tremuloides by the leaves being more coarsely toothed.
It is a very hardy species and tolerates long, cold winters and short summers.
Like other aspens, it spreads extensively by root sprouts, which may be produced up to 40 m from the parent tree, forming extensive clonal colonies.
The hybrid with Populus alba (White Poplar), known as Grey Poplar Populus × canescens, is widely found in Europe and central Asia. Hybrids with several other aspens have also been bred at forestry research institutes in order to find trees with greater timber production and disease resistance (e.g. P. tremula × P. tremuloides, bred in Denmark).
Aspen is resistant to browsing pressure by fallow deer due to its unpleasant taste.
1. ^ James Kilkelly Irish native Aspen tree
Source: Wikispecies: All text is available under the terms of the GNU Free Documentation License