title: Biomechanical and leaf-climate relationships: a comparison of ferns and seed plants.
abstract: OBJECTIVE
  Relationships of leaf size and shape (physiognomy) with climate have been well characterized for woody non-monocotyledonous angiosperms (dicots), allowing the development of models for estimating paleoclimate from fossil leaves. More recently, petiole width of seed plants has been shown to scale closely with leaf mass. By measuring petiole width and leaf area in fossils, leaf mass per area (MA) can be estimated and an approximate leaf life span inferred. However, little is known about these relationships in ferns, a clade with a deep fossil record and with the potential to greatly expand the applicability of these proxies.
  
  
  METHODS
  We measured the petiole width, MA, and leaf physiognomic characters of 179 fern species from 188 locations across six continents. We applied biomechanical models and assessed the relationship between leaf physiognomy and climate using correlational approaches.
  
  
  RESULTS
  The scaling relationship between area-normalized petiole width and MA differs between fern fronds and pinnae. The scaling relationship is best modeled as an end-loaded cantilevered beam, which is different from the best-fit biomechanical model for seed plants. Fern leaf physiognomy is not influenced by climatic conditions.
  
  
  CONCLUSIONS
  The cantilever beam model can be applied to fossil ferns. The lack of sensitivity of leaf physiognomy to climate in ferns argues against their use to reconstruct paleoclimate. Differences in climate sensitivity and biomechanical relationships between ferns and seed plants may be driven by differences in their hydraulic conductivity and/or their differing evolutionary histories of vein architecture and leaf morphology.
authors: Department of Geology, Baylor University, Waco, Texas 76798 USA.
authors: Daniel J
authors: DJ
authors: Peppe
authors: Casee R
authors: CR
authors: Lemons
authors: Dana L
authors: DL
authors: Royer
authors: Scott L
authors: SL
authors: Wing
authors: Ian J
authors: IJ
authors: Wright
authors: Christopher H
authors: CH
authors: Lusk
authors: Chazelle H
authors: CH
authors: Rhoden
mesh_terms: D005075:Biological Evolution; D001696:Biomechanical Phenomena; D002980:Climate; D029624:Ferns / Q000033:anatomy & histology*; D005580:Fossils; D019684:Magnoliopsida / Q000033:anatomy & histology*; D018515:Plant Leaves / Q000033:anatomy & histology*; D012639:Seeds
keywords: climate; ferns; leaf economic spectrum; leaf mass per area; leaf physiognomy; paleobotany; paleoecology