Hypha refers to the long filamentous branches found in fungi and actinobacteria. Hyphae are important structures required for growth in these species, and together, are referred to as mycelium.
Each hypha is comprised of at least one cell encapsulated by a protective cell wall typically made of chitin, and contain internal septa, which serve to divide the cells. Septa are important as they allow cellular organelles (ribosomes) to pass between cells via large pores. However, not all species of fungi contain septa. The average hyphae are approximately 4 to 6 microns in size.
Hyphae growth occurs by extending the cell walls and internal components from the tips. During tip growth, a specialized organelle called the spitzenkörper, assists in the formation of new cell wall and membrane structures by harboring vesicles derived from the golgi apparatus and releasing them along the apex of the hypha.
As the spitzenkörper moves, the tip of the hypha is extended via the release of the vesicle contents, which form the cell wall, and the vesicle membranes, which create a new cell membrane. As the hypha extends, new septa can be created to internally divide the cells. The characteristic branching of hyphae is the result of the formation of a new tip from a hypha, or the division of a growing tip.