title: A protocol for the creation of useful geometric shape metrics illustrated with a newly derived geometric measure of leaf circularity.
abstract: OBJECTIVE
  I present a protocol for creating geometric leaf shape metrics to facilitate widespread application of geometric morphometric methods to leaf shape measurement. •
  
  
  RESULTS
  To quantify circularity, I created a novel shape metric in the form of the vector between a circle and a line, termed geometric circularity. Using leaves from 17 fern taxa, I performed a coordinate-point eigenshape analysis to empirically identify patterns of shape covariation. I then compared the geometric circularity metric to the empirically derived shape space and the standard metric, circularity shape factor. •
  
  
  CONCLUSIONS
  The geometric circularity metric was consistent with empirical patterns of shape covariation and appeared more biologically meaningful than the standard approach, the circularity shape factor. The protocol described here has the potential to make geometric morphometrics more accessible to plant biologists by generalizing the approach to developing synthetic shape metrics based on classic, qualitative shape descriptors.
authors.affiliation: Herbarium, Library, Art and Archives Directorate, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Krieger
keywords: eigenshape analysis; geometric morphometrics; leaf physiognomy; leaf shape