Coding Meristic Characters for Phylogenetic Analysis: A Comparison of Step-Matrix Gap-Weighting and Generalized Frequency Coding

Meristic characters, or counts of discrete serially ho-mologous structures, are a distinctive and ubiquitous class of quantitative organismal variation. Meristic char-acters share many properties with morphometric char-acters (i.e., measurements, proportions, etc.): they are readily described numerically, they usually vary within and among taxa, and they often appear to follow similar underlying frequency distributions (e.g., Burbrink, 2001; Allsteadt et al., 2006). Based on these similarities, meris-tic characters are generally lumped with morphometric characters into the broader category of “quantitative con-tinuous characters ” for phylogeny reconstruction. Meris-tic characters also exhibit properties that differ subtly, but perhaps importantly, from morphometric characters. It has been increasingly recognized that morphologica