There are only 11 published reports of crystals in the large family Rosaceae. Except for an undocumented mention of raphides in Quillaja, only druses and prismatics are known. There are only three brief reports for Prunus s.l. (150-200 species; Subfamily Prunoideae). We found previously unreported large adaxial, sub-epidermal, crystal idioblasts with prismatics in leaves of Prunus virginiana (choke cherry), which prompted us to survey 86 species of all subgenera and sections of Prunus s.l., as well as two species of Quillaja. Small leaf samples taken mostly from herbarium specimens were re-hydrated, partially cleared in full-strength commercial bleach to preserve the crystals, rinsed thoroughly, dehydrated, and permanently mounted. Samples viewed between crossed polarizers using light microscopy showed crystal types and sizes, location, and frequency. Dried or liquid-preserved leaf samples of selected species were either broken in cross section or peeled paradermally to expose the mesophyll and veins for scanning electron microscopy observations. Druses (spherical aggregates of crystals) are most common by far, typically in bundle sheath cells, but in some species also in scattered mesophyll cells. Prismatics are less common, usually among druses, but occuring in large sub-epidermal idioblasts in a few species, of which P. virginiana and P. padus are the best examples. P. serotina has myriad small prismatics almost exclusively. This as yet incomplete survey, a rarely done type of crystal study, indicates that crystals are potentially useful taxonomic characters at sub-generic levels in Prunus. The survey is also a useful frame of reference for more intensive microscopic study on Prunus crystals, which is in progress.

Key words: calcium oxalate, crystal distribution, leaves, Prunus