Complex sentence: The medulla (a loosely arranged layer of hyphae below the cortex and photobiont zone) is whitish but lower part red; it has few to many calcium oxalate crystals that are 3--8 μm diameter.
Split into simpler sentences: The medulla (a loosely arranged layer of hyphae below the cortex and photobiont zone) is whitish but the lower part is red. It has few to many calcium oxalate crystals that are 3--8 μm diameter.