Conidia on conidiophores. A hypha (plural hyphae, from Greek ὑφή, huphḗ, “web”) is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.Yeasts are unicellular fungi that do not grow as hyphae.n most fungi, hyphae are divided into cells by internal cross-walls called septa (singular septum). Septa are usually perforated by pores large enough for ribosomes, mitochondria and sometimes nuclei to flow between cells.