Towards uncovering evolution of lineage-specific calcium oxalate crystal patterns in Piperales

Abstract

Piperales is among the largest and most diverse angiosperm orders (>4000 species), occurring broadly in tropical and temperate habitats. Twenty-four of the species from 12 genera, representing all lineages of Piperales, except the holoparasitic Hydnoraceae, display a mixture of leaf calcium oxalate crystal types found in previous studies of the two genera of Piperaceae subfamily Piperoideae (Peperomia Ruiz & Pav. and Piper L.). Crystal macropatterns, a result of varying leaf anatomies and diverse habitats, are investigated in a comparative way by using clearings and recent molecular phylogenetic hypotheses to trace crystal types and macropattern evolution. Ancestral character reconstruction reveals that the most recent common ancestor of Piperales had either crystal sand or druses or both and that prisms, raphides, and styloids are derived from the ancestral crystal type(s). These results are also recovered for both the ancestors of the perianth-less and the perianth-bearing Piperales. Raphides or druses are found in the two other subfamilies of Piperaceae (Verhuellioideae and Zippelioideae). Asaraceae and Lactoridaceae display crystal sand, whereas Aristolochia L. (Aristolochiaceae) species display mainly druses. Our crystal investigation, combined with ancestral character reconstruction, suggests that styloids, raphides, and prisms are derived within Piperales from crystal sand or druses.