Wood anatomical diversity results from force of habit, and shifts in habitat

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Plant functional traits constitute responses to a complex evolutionary reciprocality between plants and the environment. Wood anatomy varies between shrubs and trees, and between wet and dry habitats, but a question remains as to the degree to which growth habit and habitat shape and are in turn shaped by wood structure. Using phylogenetic comparative methods, Arévalo et al. tested for contingent evolution of wood anatomy, habit, and habitat in the mega-diverse angiosperm genus Croton (Euphorbiaceae), which possesses a growth habit manifesting in most species as persistently woody shrubs and small to large trees.

Images (including light micrographs) of character states (unequivocal and equivocal) present in ancestral Croton inferred via ancestral state reconstruction.
Images (including light micrographs) of character states (unequivocal and equivocal) present in ancestral Croton inferred via ancestral state reconstruction. (A) Croton macrobothrys (Mata Atlantica, Bahia, Brazil) depicting the tree habit; (B) confluent-like axial parenchyma; (C) disjunctive ray parenchyma cell walls; (D) nominal procumbent ray cells; (E) mesic habitat depicted by C. rimbachii (Oxapampa Province, Pasco Region, Peru), and xeric habitat depicted by C. thurifer (Utcubamba Province, Amazonas Region, Peru); (F) vessels in radial arrangement; (G) > 4 cells per parenchyma strand; (H) perforated ray cells (asterisk) and crystals in upright ray cells (arrowheads); (I) true procumbent ray cells. Scale bars = 200 µm.

Showing that habit and habitat influence wood anatomical evolution and that wood anatomy affects shifts in habit and habitat, the study presents a set of novel functional trait associations for woody plant structure. The only wood anatomical trait correlated with habitat and not habit was the presence of helical thickenings in the vessel elements of mesic Croton.

Reference

Arévalo, R., van Ee, B. W., Riina, R., Berry, P. E., & Wiedenhoeft, A. C. (2017). Force of habit: shrubs, trees and contingent evolution of wood anatomical diversity using Croton (Euphorbiaceae) as a model system. Annals of Botany, mcw243. https://doi.org/10.1093/aob/mcw243


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