Leaf Surface Microstructure, Anatomical Characteristics and Cystoliths of Phlogacanthus pulcherrimus T. Anderson

Phlogacanthus pulcherrimus T. Anderson is a medicinal and edible plant in the family Acanthaceae. The leaf extract possesses anti-breast cancer activity and is rich in essential nutrients and minerals. Calcium can accumulate in the plant cells when the plant receives an excess of calcium from the soil. The deposited calcium is usually in the form of calcium carbonate (CaCO3), called cystoliths. The leaves of most Acanthaceae plants have characteristic distributions of cystoliths, which can be used for plant species identification. Anatomical characteristics are crucial for identifying medicinal plants, as similar morphology among species in the same genus can lead to misidentification and affect the proper use of active compounds. This study aimed to examine the leaf surface structures of the Phlogacanthus medicinal plant species, specifically cystolith crystals in the lithocyst of P. pulcherrimus leaves. Several analytical techniques were used: light microscopes, a polarized microscope, and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The results revealed that the stomata appeared only on the lower epidermis. The stomatal characteristics were of the diacytic type, with two subsidiary cells arranged perpendicularly to a pair of guard cells. The cystolith is a calcium carbonate (CaCO3) deposit formed within a specialized cell called a lithocyst. The cystoliths (CaCO3 crystals) occurred in epidermal lithocysts of the leaf blade and in the hypodermal cells of the midrib. A large crystal with a rounded shape was found in a lithocyst. EDS spectra and maps obtained from the cystolith crystals showed the presence of calcium (Ca), oxygen (O), and silicon (Si) elements. The leaf surface microstructure and crystal morphological characteristics are important and beneficial for identifying the P. pulcherrimus medicinal plants.