Early evidence of xeromorphy in angiosperms: Stomatal encryption in a new eocene species of Banksia (Proteaceae) from Western Australia

Carpenter, R. J. and McLoughlin, S. and Hill, R. S. and McNamara, K. J. and Jordan, G. J. (2014) Early evidence of xeromorphy in angiosperms: Stomatal encryption in a new eocene species of Banksia (Proteaceae) from Western Australia. American Journal of Botany, 101 (9). pp. 1486-1497. ISSN 0002-9122 DOI 10.3732/ajb.1400191

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Official URL: http://dx.doi.org/10.3732/ajb.1400191

Abstract

• Premise of the study: 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. • Key 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.

Item Type: Article
Uncontrolled Keywords: 2014AREP, IA68,
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
07 - Gold Open Access
Journal or Publication Title: American Journal of Botany
Volume: 101
Page Range: pp. 1486-1497
Identification Number: 10.3732/ajb.1400191
Depositing User: Sarah Humbert
Date Deposited: 02 Nov 2014 02:07
Last Modified: 20 Nov 2014 13:39
URI: http://eprints.esc.cam.ac.uk/id/eprint/3147

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