Abstract
PremiseDespite intensive research, the pathways and driving forces behind the evolution of derived woodiness on oceanic islands remain obscure. The genus Daucus comprises mostly herbs (therophytes, hemicryptophytes) with few rosette treelets (chamaephytes) endemic to various Macaronesian archipelagos, suggesting their independent evolution. To elucidate the evolutionary pathways to derived woodiness, we examined phylogenetic relationships and the habit and secondary xylem evolution in Daucus and related taxa.MethodsSixty taxa were surveyed for molecular markers, life history, and habit traits. Twenty‐one species were considered for wood anatomical characters. A dated phylogeny was estimated using Bayesian methods. The evolution of selected traits was reconstructed using parsimony and maximum likelihood.Results Daucus dispersed independently to the Canary Islands (and subsequently to Madeira), Cape Verde, and the Azores in the late Miocene and Pleistocene. Life span, reproductive strategy, and life form were highly homoplastic; the ancestor of Daucus was probably a monocarpic, biennial hemicryptophyte. Rosette treelets evolved independently in the Canarian‐Madeiran lineage and in Cape Verde, the latter within the last 0.13 Myr. Treelets and hemicryptophytes did not differ in wood anatomy. Pervasive axial parenchyma in wood occurred more often in polycarpic rather than monocarpic species.ConclusionsLife span and life form in Daucus are evolutionarily labile and may change independently of wood anatomy, which is related to plant reproductive strategy rather than to life form. Insular woodiness may evolve rapidly (as demonstrated in D. bischoffii), and in Daucus, it does not seem to be an adaptation to lower the risk of xylem embolism.
Highlights
Insular woodiness may evolve rapidly, and in Daucus, it does not seem to be an adaptation to lower the risk of xylem embolism
Woodiness was most likely ancestral within angiosperms, and the shift from trees and shrubs to herbs has long been considered a major trend in the evolution of flowering plants (e.g., Sinnott and Bailey, 1915); a large body of evidence suggests that the opposite is possible and that many woody taxa in various angiosperm lineages originated from herbaceous ancestors
Darwin suggested increased competition between herbaceous species favoring taller individuals; Carlquist (1974) postulated that moderate climates with low seasonality and/or the absence of large herbivores may be responsible for the shift; and recently, Lens et al (2013b) and Dória et al (2018) considered drought adaptation to be the trigger because derived woody stems have higher embolism resistance than herbaceous relatives
Summary
Frankiewicz1,7 , Alexei Oskolski, Łukasz Banasiak, Francisco Fernandes, Jean-Pierre Reduron, Jorge-Alfredo Reyes-Betancort, Liliana Szczeparska, Mohammed Alsarraf, Jakub Baczyński, and Krzysztof Spalik. PREMISE: Despite intensive research, the pathways and driving forces behind the evolution of derived woodiness on oceanic islands remain obscure. The genus Daucus comprises mostly herbs (therophytes, hemicryptophytes) with few rosette treelets (chamaephytes) endemic to various Macaronesian archipelagos, suggesting their independent evolution. To elucidate the evolutionary pathways to derived woodiness, we examined phylogenetic relationships and the habit and secondary xylem evolution in Daucus and related taxa
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