Classification
The genus Populus has traditionally been divided into six sections on the basis of leaf and flower characters; this classification is followed below. Recent genetic studies have largely supported this, confirming some previously suspected reticulate evolution due to past hybridisation and introgression events between the groups. Some species (noted below) had differing relationships indicated by their nuclear DNA (paternally inherited) and chloroplast DNA sequences (maternally inherited), a clear indication of likely hybrid origin. Hybridisation continues to be common in the genus, with several hybrids between species in different sections known.
Read more about this topic: Poplar