Final Activity Report Summary - SALIX (World classification and phylogeny of Salicaceae s. str.)
The willow family, including willows, poplars, aspen and cottonwoods, has always been one of the most difficult to understand and classify. The objective of this research was to combine the existing regional classifications into a worldwide classification using the literature, morphological characters and investigating the phylogenetic relationships using molecular markers.
The DNA from a large number of species representing plants from all groups of the willow family, from all regions around the world and growing in different ecological habitats was extracted, analysed and saved in the DNA bank at Kew. The most important result that explains the difficulties in identification and classification of the willow family is that most of the taxa from genera to species level are non-monophyletic which could have resulted from gene duplication, lineage sorting or hybridisation. The use of a low copy nuclear gene, ADH (alcohol dehydrogenase), allowed us to investigate which species share the same ancestoral characters and therefore the routes of their evolution. As a result of this research, in some cases, we can say which species evolved from hybridisation events. However, the classification based on morphology is not the same as the one we have got from this molecular analysis. According to the molecular data all the genera of the willow family (willows, poplars, aspens and cottonwoods) should form a single genus which is in disagreement with their morphology.
To resolve this incongruence much more research at the population level is required. Until then it is not possible to make any new classification into groups in the willow family. However, the worldwide checklist of species that has been produced will be even more useful in the light of the above mentioned results to help in the establishment of local floras. Interactive keys for the willow family (genera and species levels) will be published on the internet shortly.
The DNA from a large number of species representing plants from all groups of the willow family, from all regions around the world and growing in different ecological habitats was extracted, analysed and saved in the DNA bank at Kew. The most important result that explains the difficulties in identification and classification of the willow family is that most of the taxa from genera to species level are non-monophyletic which could have resulted from gene duplication, lineage sorting or hybridisation. The use of a low copy nuclear gene, ADH (alcohol dehydrogenase), allowed us to investigate which species share the same ancestoral characters and therefore the routes of their evolution. As a result of this research, in some cases, we can say which species evolved from hybridisation events. However, the classification based on morphology is not the same as the one we have got from this molecular analysis. According to the molecular data all the genera of the willow family (willows, poplars, aspens and cottonwoods) should form a single genus which is in disagreement with their morphology.
To resolve this incongruence much more research at the population level is required. Until then it is not possible to make any new classification into groups in the willow family. However, the worldwide checklist of species that has been produced will be even more useful in the light of the above mentioned results to help in the establishment of local floras. Interactive keys for the willow family (genera and species levels) will be published on the internet shortly.