title: A comparison of leaf crystal macropatterns in the two sister genera Piper and Peperomia (Piperaceae).
abstract: OBJECTIVE
  This is the first large-scale study comparing leaf crystal macropatterns of the species-rich sister genera Piper and Peperomia. It focuses on identifying types of calcium oxalate crystals and their macropatterns in leaves of both genera. The Piper results are placed in a phylogenetic context to show evolutionary patterns. This information will expand knowledge about crystals and provide specific examples to help study their form and function. One example is the first-time observation of Piper crystal sand tumbling in chlorenchyma vacuoles.
  
  
  METHODS
  Herbarium and fresh leaves were cleared of cytoplasmic content and examined with polarizing microscopy to identify types of crystals and their macropatterns. Selected hydrated herbarium and fresh leaf punches were processed for scanning electron microscopy and x-ray elemental analysis. Vibratome sections of living Piper and Peperomia leaves were observed for anatomical features and crystal movement.
  
  
  RESULTS
  Both genera have different leaf anatomies. Piper displays four crystal types in chlorenchyma-crystal sand, raphides, styloids, and druses, whereas Peperomia displays three types-druses, raphides, and prisms. Because of different leaf anatomies and crystal types between the genera, macropatterns are completely different. Crystal macropattern evolution in both is characterized by increasing complexity, and both may use their crystals for light gathering and reflection for efficient photosynthesis under low-intensity light environments.
  
  
  CONCLUSIONS
  Both genera have different leaf anatomies, types of crystals and crystal macropatterns. Based on Piper crystals associated with photosynthetic tissues and low-intensity light, further study of their function and association with surrounding chloroplasts is warranted, especially active crystal movement.
authors.affiliation: Department of Genetics, Development and Cell Biology & Microscopy and NanoImaging Facility, Iowa State University, Ames, Iowa 50011-1020 USA.
authors.forename: Harry T
authors.initials: HT
authors.lastname: Horner
authors.forename: Stefan
authors.initials: S
authors.lastname: Wanke
authors.forename: Marie-Stéphanie
authors.initials: MS
authors.lastname: Samain
mesh_terms: D002129:Calcium Oxalate / Q000737:chemistry*; D003460:Crystallization; D008855:Microscopy, Electron, Scanning; D008859:Microscopy, Polarization; D018715:Microscopy, Video; D036941:Peperomia / Q000737:chemistry* / Q000145:classification; D031701:Piper / Q000737:chemistry* / Q000145:classification; D018515:Plant Leaves / Q000737:chemistry* / Q000648:ultrastructure; D013045:Species Specificity
chemical_list: D002129:Calcium Oxalate