A druse is a group of crystals of calcium oxalate, silicates, or carbonates present in plants, and are thought to be a defense against herbivory due to their toxicity. Calcium oxalate (Ca(COO)2, CaOx) crystals are found in algae, angiosperms and gymnosperms in a total of more than 215 families. These plants accumulate oxalate in the range of 3–80% (w/w) of their dry weight through a biomineralization process in a variety of shapes. Araceae have numerous druses, multi-crystal druses and needle-shaped raphide crystals of CaOx present in the tissue. Druses are also found in leaves and bud scales of Prunus, Rosa, Allium, Vitis, Morus and Phaseolus.

An idioblast is an isolated plant cell that differs from neighboring tissues. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin, tannin, or pigments etc. Some can contain mineral crystals such as acrid tasting and poisonous calcium oxalate, carbonate, or silica. Any of the tissue or tissue systems of plants can contain idioblasts. Idioblasts are divided into three main categories: excretory, tracheoid, and sclerenchymatous.