Calcium oxalate crystals in monocotyledons: A review of their structure and systematics

Three main types of calcium oxalate crystal occur in monocotyledons: raphides, styloids and druses, although intermediates are sometimes recorded. The presence or absence of the different crystal types may represent 'useful' taxonomic characters. For instance, styloids are characteristic of some families of Asparagales, notably Iridaceae, where raphides are entirely absent. The presence of styloids is therefore a synapomorphy for some families (e.g. Iridaceae) or groups of families (e.g. Philydraceae, Pontederiaceae and Haemodoraceae). This paper reviews and presents new data on the occurrence of these crystal types, with respect to current systematic investigations on the monocotyledons. (C) 1999 Annals of Botany Company.