A review of anatomical and phytolith studies of cystoliths: silica-calcium phytoliths in dicotyledonous angiosperms.

Cystoliths are phytoliths of silica and calcium carbonate and are produced in a few groups of dicotyledonous angiosperms. Anatomical and, more recently, phytolith studies have recorded them in different families. In the present review, we analyse and integrate both types of research to compile information about their formation and composition, their distribution in vascular plants, their relation with anatomy and systematics and their potential roles in plant tissues. We also include analyses of specimens belonging to families having poorly-known cystolith information. According to our review, cystoliths can be considered to be Si-Ca phytoliths. They are well described in eight families, and in 14 other families the information is inconclusive. The production of cystoliths is limited to dicotyledons, but there is no clear phylogenetic relation between the families that produce them. Cystolith accumulation is predominantly in the epidermis of leaves and/or in parenchymatic rays of woods. Diverse roles related to photosynthesis enhancement and as Ca reservoirs have been assigned to cystoliths. Knowledge of cystolith production among vascular plants is relevant for anatomical, systematic and ecological research, and also for biogeochemical studies due to their importance as a source of Ca and Si. [ABSTRACT FROM AUTHOR]