title: Early evidence of xeromorphy in angiosperms: stomatal encryption in a new eocene species of Banksia (Proteaceae) from Western Australia.
abstract: •
  
  
  OBJECTIVE
  Globally, the origins of xeromorphic traits in modern angiosperm lineages are obscure but are thought to be linked to the early Neogene onset of seasonally arid climates. Stomatal encryption is a xeromorphic trait that is prominent in Banksia, an archetypal genus centered in one of the world's most diverse ecosystems, the ancient infertile landscape of Mediterranean-climate southwestern Australia.•
  
  
  METHODS
  We describe Banksia paleocrypta, a sclerophyllous species with encrypted stomata from silcretes of the Walebing and Kojonup regions of southwestern Australia dated as Late Eocene.•
  
  
  RESULTS
  Banksia paleocrypta shows evidence of foliar xeromorphy ∼20 Ma before the widely accepted timing for the onset of aridity in Australia. Species of Banksia subgenus Banksia with very similar leaves are extant in southwestern Australia. The conditions required for silcrete formation infer fluctuating water tables and climatic seasonality in southwestern Australia in the Eocene, and seasonality is supported by the paucity of angiosperm closed-forest elements among the fossil taxa preserved with B. paleocrypta. However, climates in the region during the Eocene are unlikely to have experienced seasons as hot and dry as present-day summers.•
  
  
  CONCLUSIONS
  The presence of B. paleocrypta within the center of diversity of subgenus Banksia in edaphically ancient southwestern Australia is consistent with the continuous presence of this lineage in the region for ≥40 Ma, a testament to the success of increasingly xeromorphic traits in Banksia over an interval in which numerous other lineages became extinct.
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia School of Earth and Environmental Sciences, Benham Bldg DX 650 312, University of Adelaide, South Australia 5005, Australia.
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Carpenter
authors.affiliation: Department of Palaeobiology, Swedish Museum of Natural History, Box 50007 104 05 Stockholm, Sweden.
authors.forename: Stephen
authors.initials: S
authors.lastname: McLoughlin
authors.affiliation: School of Earth and Environmental Sciences, Benham Bldg DX 650 312, University of Adelaide, South Australia 5005, Australia South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Hill
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: McNamara
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia.
authors.forename: Gregory John
authors.initials: GJ
authors.lastname: Jordan
mesh_terms: D000222:Adaptation, Physiological; D005075:Biological Evolution; D002980:Climate; D055864:Droughts; D005580:Fossils; D019684:Magnoliopsida; D010802:Phylogeny; D018515:Plant Leaves / Q000033:anatomy & histology; D054046:Plant Stomata / Q000033:anatomy & histology*; D039105:Proteaceae / Q000033:anatomy & histology / Q000235:genetics; D012621:Seasons; D013696:Temperature; D014867:Water; D014904:Western Australia
chemical_list: D014867:Water
keywords: Banksia; Eocene; Proteaceae; sclerophylly; silcrete; southwestern Australia; stomatal crypt; xeromorphy