Insular woodiness (IW), referring to the evolutionary transition from herbaceousness toward woodiness on islands, has arisen more than 30 times on the Canary Islands (Atlantic Ocean). One of the IW... Show moreInsular woodiness (IW), referring to the evolutionary transition from herbaceousness toward woodiness on islands, has arisen more than 30 times on the Canary Islands (Atlantic Ocean). One of the IW hypotheses suggests that drought has been a major driver of wood formation, but we do not know in which palaeoclimatic conditions the insular woody lineages originated. Therefore, we provided an updated review on the presence of IW on the Canaries, reviewed the palaeoclimate, and estimated the timing of origin of woodiness of 24 insular woody lineages that represent a large majority of the insular woody species diversity on the Canaries. Our single, broad-scale dating analysis shows that woodiness in 60%–65% of the insular woody lineages studied originated within the last 3.2 Myr, during which Mediterranean seasonality (yearly summer droughts) became established on the Canaries. Consequently, our results are consistent with palaeoclimatic aridification as a potential driver of woodiness in a considerable proportion of the insular woody Canary Island lineages. However, the observed pattern between insular woodiness and palaeodrought during the last couple of million years could potentially have emerged as a result of the typically young age of the native insular flora, characterized by a high turnover. Show less
Lens, F.P.; Davin, N.F.; Smets, E.F.; Arco, M. del 2013
Premise of research. One of the most conspicuous aspects of island floras is the relatively high proportion of woody species. Often, but not always, these woody species have developed wood on the... Show morePremise of research. One of the most conspicuous aspects of island floras is the relatively high proportion of woody species. Often, but not always, these woody species have developed wood on the islands and have evolved from herbaceous continental ancestors, a phenomenon known as insular woodiness. Shifts from herbaceousness toward increased woodiness also occur on continents (the broader term “secondary woodiness” is more appropriate here and includes insular woodiness), but comprehensive worldwide knowledge about secondary woodiness within angiosperms remains lacking. We update hypotheses regarding the herbaceous ancestry of woody Canarian lineages in a molecular phylogenetic context and investigate the possible link of secondary woodiness and paedomorphic wood features in the Carlquistian sense. Methodology. We have assembled available literature data from molecular phylogenetic studies, wood anatomical descriptions, floras, and taxonomic revisions to identify the native secondarily woody taxa. Pivotal results. In total, at least 220 native Canary Island species of flowering plants, from 34 genera representing 15 families, are truly insular woody. This represents a significant portion of the native nonmonocot angiosperm species on the Canaries, and all of the insular woody species have paedomorphic wood features in the Carlquistian sense, although this wood anatomical syndrome might be more related to particular life forms. The majority of these insular woody groups typically grow in the markedly dry lowland regions, suggesting a possible link between secondary woodiness and increased drought resistance. Conclusions. The Canary Island flora is characterized by at least 38 independent shifts toward insular woodiness, representing an important portion of the endemic angiosperms on the archipelago. These convergent evolutionary events emphasize the remarkable lability in growth forms between herbaceous and woody lineages, but it remains puzzling which environmental variables trigger these shifts and how these independent shifts are regulated genetically. Show less
