Cystoliths in the leaves of the genus Pseuderanthemum (Acanthaceae) in Thailand

Abstract

The morphology and distribution of calcium carbonate crystals or cystoliths in mature leaves of fifteen taxa, included 2 exotic species of the genus Pseuderanthemum (Acanthaceae) in Thailand were studied. All studied taxa contained calcium crystals. The size of cystoliths varied even in the same species. The crystals ranged from 65 mm to 300 mm in length and 17.5 mm to 100 mm in breadth. Length and breadth ratio of cystoliths varied for the genus, but the ratio of the most common type of cystoliths, i.e., elongated, tapering at one end remains constant. The cystoliths in the leaves were mainly found as eyebrow-shaped or rod-shaped crystals. Their shape was classified to seven categories. All calcium carbonate crystals or cystoliths were located in the epidermal lithocysts. In the leaves of Pseuderanthemum, cystoliths mostly occurred in the adaxial epidermis; however, the cystoliths in Pseuderanthemum axillare were located equally in both surfaces. The orientation of cystoliths can occur in two forms: (a) cystoliths arranged randomly in central area, and (b) cystoliths arranged parallel to midrib and leaf margin.