Arbuscular mycorrhizal fungi are special underground fungi that form partnerships with plant roots to help plants grow. Unlike most cells, these fungi form long, tube-like structures without walls dividing them into sections, allowing nutrients and other materials to flow freely throughout their networks. This review explains how these fungi are built at the cellular level, including their walls, membranes, and internal structures, helping scientists better understand how they exchange nutrients with plants and contribute to healthy ecosystems.