Anatomical Characteristics of Leaf and Petiole and Presence of Calcium Oxalate Crystals in Giant Elephant Ear (Colocasia gigantea (Blume) Hook. f.)

The genus Colocasia contains mostly calcium oxalate (CaOX), especially found in petioles and leaves. The petioles of C. gigantea are usually consumed by Southeast Asian people for cooking. In addition, fresh petioles together with leaves are utilized as animal feed. This study aims to determine the anatomical characteristics of both parts of the above mentioned to identify characters of CaOX crystals using a compound light microscope, polarized microscope, scanning electron microscope, and energy-dispersive X-ray spectrometer. The results showed that the leaf anatomical characteristics comprise four layers, i.e. the upper and the lower epidermis, mesophyll, and vascular bundles, respectively. The mesophyll layer consists of palisade cells, spongy cells, and air spaces. Besides the idioblast cells also found in the mesophyll. The petiole comprises three layers, i.e. the epidermis, stele (vascular bundle), and cortex where parenchyma cells, air spaces, and idioblast cells exist. The idioblast cells contain a group of raphide (or raphide bundle) of CaOX in the cell. The palisade cells of the leaf and parenchyma cells of the petiole contain other shapes of CaOX crystals such as druse, rectangular prism, hexagonal prism, and octahedron prism. The length and thickness of the raphide crystals bundle are 60.40-67.50 μm and 26.00-30.90 μm, respectively. The length and thickness of needle-like crystals are 20.80- 67.30 μm and 0.86-1.04 μm, respectively. The diameter of crystals in a druse form is 25.70-30.60 μm. The small crystals appear in three forms, i.e. rectangular, hexagonal, and octagonal prism. The length, width, and thickness of crystals are 3.57-6.57 μm, 1.11-2.05 μm, and 0.33-2.61 μm, respectively. The EDS X-ray spectra and maps analyzed from the crystals found the elements of calcium (Ca) and oxygen (O).