Phylomineralogy of the Coralline red algae: Correlation of skeletal mineralogy with molecular phylogeny

► This is the first report of appreciable amounts of aragonite in coralline algae. ► Mineralogical variability is greatest in the Hapalidiaceae, especially the genus Mesophyllum. ► Articulated forms are usually calcitic; crustose forms may show some aragonite. ► Mg in calcite varies among families, but is not a useful taxonomic character. ► Algal Mg calcites are vulnerable to ocean acidification, especially in cool waters.