Data from: Biomechanical and leaf-climate relationships: a comparison of ferns and seed plants

Premise of the study: 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. Key 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.