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Front. Plant Sci. | doi: 10.3389/fpls.2018.00197

Geometry, allometry and biomechanics of fern leaf petioles: their significance for the evolution of functional and ecological diversity within the Pteridaceae

 Jennifer Mahley1,  Jarmila Pittermann1*,  Nick Rowe2, Alex Baer3,  James Watkins4,  Eric Schuettpelz5, James K. Wheeler1,  Klaus Mehltreter6, Michael Windham7,  Weston Testo8 and James Beck9
  • 1Ecology and Evolutionary Biology, University of California, Santa Cruz, United States
  • 2UMR-AMAP, Université de Montpellier, France
  • 3Department of Biology, California State University, Bakersfield, United States
  • 4Department of Biology, Colgate University, United States
  • 5National Museum of Natural History, Smithsonian Institution (SI), United States
  • 6Departamento Ecologia Vegetal, Institute of Ecology (INECOL), Mexico
  • 7Department of Biology, Duke University, United States
  • 8Department of Plant Biology, University of Vermont, United States
  • 9Biological Sciences, Wichita State University, United States

Herbaceous plants rely on a combination of turgor, ground tissues and geometry for mechanical support of leaves and stems. Unlike most angiosperms however, ferns employ a sub-dermal layer of fibers, known as a hypodermal sterome, for support of their leaves. The sterome is nearly ubiquitous in ferns, but nothing is known about its role in leaf biomechanics. The goal of this research was to characterize sterome attributes in ferns that experience a broad range of mechanical stresses, as imposed by their aquatic, xeric, epiphytic and terrestrial niches. Members of the Pteridaceae meet this criteria well. The anatomical and functional morphometrics along with published values of tissue moduli were used to model petiole flexural rigidity and susceptibility to buckling in 20 species of the Pteridaceae. Strong allometric relationships were observed between sterome thickness and leaf size, with the sterome contributing over 97% to petiole flexural rigidity. Surprisingly, the small-statured cheilanthoid ferns allocated the highest fraction of their petiole to the sterome, while large leaves exploited aspects of geometry (second moment of area) to achieve bending resistance. This pattern also revealed an economy of function in which increasing sterome thickness was associated with decreasing fiber cell reinforcement, and fiber wall fraction. Lastly, strong petioles were associated with durable leaves, as approximated by specific leaf area. This study reveals meaningful patterns in fern leaf biomechanics that align with species leaf size, sterome attributes and life-history strategy.

Keywords: Sclerenchyma, ground tissue, Flexural rigidity, Modulus of elasticity, Second moment of area

Received: 01 Jul 2017; Accepted: 01 Feb 2018.

Edited by:

Katrin Kahlen, Hochschule Geisenheim University, Germany

Reviewed by:

Fulton Rockwell, Harvard University, United States
Evelyne Costes, INRA UMR Amélioration génétique et adaptation des plantes méditerranéennes et tropicales, France
Ian Stavness, University of Saskatchewan, Canada  

Copyright: © 2018 Mahley, Pittermann, Rowe, Baer, Watkins, Schuettpelz, Wheeler, Mehltreter, Windham, Testo and Beck. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Ms. Jarmila Pittermann, University of California, Santa Cruz, Ecology and Evolutionary Biology, 1156 High Street, Santa Cruz, 95064, California, United States, jpitterm@ucsc.edu