A poplar was the first tree ever to have its whole genome read
In 2006 the western balsam poplar became the first tree to have its complete DNA sequenced. It belongs to Populus, a genus of 61 accepted species of poplars, aspens and cottonwoods whose flattened leaf stalks make whole trees shimmer in a breeze, and whose ancestry is tangled by constant hybridisation.
Populus belongs to the willow family and grows across temperate, subarctic and mountain regions of Eurasia, North America and North Africa, plus the tropical highlands of East Africa. Species range from 15 to 50 metres tall, with trunks up to 2.5 metres across. Young bark is smooth, pale or grey-green and dotted with breathing pores called lenticels; in some species it stays smooth with age, while in others it becomes rough and deeply furrowed. Unlike willows, poplar shoots keep a bud at the tip.
The famous flicker has a mechanical cause. In the aspens and black poplars, each leaf stalk is flattened from side to side, so the slightest wind sets the blade rocking and the canopy seems to twinkle. Leaves vary greatly even on one tree, small on side shoots and very large on vigorous leading shoots, and they often turn gold before falling in autumn.
Most species have separate male and female trees. Flowers appear in early spring before the leaves, hanging in long catkins; male flowers carry anywhere from four to 60 stamens and have no petals at all. The wind does the pollinating, and female catkins stretch noticeably as they ripen. By midsummer the capsules split to release tiny seeds wrapped in long, soft white hairs, the fluff that gives cottonwoods their name and carries seeds on the breeze.
Botanists traditionally split the genus into six sections using leaves and flowers, and genetic work has broadly confirmed them while revealing a history of interbreeding. Some species, including the European black poplar, sit in one section according to their nuclear DNA but in another according to maternally inherited chloroplast DNA, a strong sign of hybrid origins. Crosses between sections still happen. The lineage is ancient: recognisable fossils of Populus wilmattae come from North America around 58 million years ago, and Cretaceous finds have turned up in Tibet and Heilongjiang in China.
Source: Populus
