title: Force of habit: shrubs, trees and contingent evolution of wood anatomical diversity using Croton (Euphorbiaceae) as a model system.
abstract: Wood is a major innovation of land plants, and is usually a central component of the body plan for two major plant habits: shrubs and trees. Wood anatomical syndromes vary between shrubs and trees, but no prior work has explicitly evaluated the contingent evolution of wood anatomical diversity in the context of these plant habits.
  
  
  
  Phylogenetic comparative methods were used to test for contingent evolution of habit, habitat and wood anatomy in the mega-diverse genus Croton (Euphorbiaceae), across the largest and most complete molecular phylogeny of the genus to date.
  
  
  
  Plant habit and habitat are highly correlated, but most wood anatomical features correlate more strongly with habit. The ancestral Croton was reconstructed as a tree, the wood of which is inferred to have absent or indistinct growth rings, confluent-like axial parenchyma, procumbent ray cells and disjunctive ray parenchyma cell walls. The taxa sampled showed multiple independent origins of the shrub habit in Croton , and this habit shift is contingent on several wood anatomical features (e.g. similar vessel-ray pits, thick fibre walls, perforated ray cells). The only wood anatomical trait correlated with habitat and not habit was the presence of helical thickenings in the vessel elements of mesic Croton .
  
  
  
  Plant functional traits, individually or in suites, are responses to multiple and often confounding contexts in evolution. By establishing an explicit contingent evolutionary framework, the interplay between habit, habitat and wood anatomical diversity was dissected in the genus Croton . Both habit and habitat influence the evolution of wood anatomical characters, and conversely, the wood anatomy of lineages can affect shifts in plant habit and habitat. This study hypothesizes novel putatively functional trait associations in woody plant structure that could be further tested in a variety of other taxa.
authors.affiliation: Center for Wood Anatomy Research, USDA Forest Service, Forest Products Laboratory, Madison, WI 53726, USA.|Department of Botany, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Rafael
authors.initials: R
authors.lastname: Arévalo
authors.affiliation: University of Puerto Rico at Mayagüez Herbarium, Department of Biology, Universidad de Puerto Rico, Call Box 9000, Mayagüez, 00680, Puerto Rico.
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: van Ee
authors.affiliation: Real Jardín Botánico, RJB-CSIC, Plaza de Murillo 2, 28014 Madrid, Spain.
authors.forename: Ricarda
authors.initials: R
authors.lastname: Riina
authors.affiliation: University of Michigan, Ecology and Evolutionary Biology Department and Herbarium, Ann Arbor, MI 48108, USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Berry
authors.affiliation: Center for Wood Anatomy Research, USDA Forest Service, Forest Products Laboratory, Madison, WI 53726, USA.|Department of Botany, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Alex C
authors.initials: AC
authors.lastname: Wiedenhoeft
mesh_terms: D044822:Biodiversity; D005075:Biological Evolution; D029802:Croton / Q000033:anatomy & histology*; D017753:Ecosystem; D010802:Phylogeny; D014197:Trees / Q000033:anatomy & histology*; D014934:Wood / Q000033:anatomy & histology*
keywords: Character state reconstruction; Croton; Euphorbiaceae; contingent evolution; functional traits; habit; habitat; phylogenetic comparative methods; wood anatomy