Fungal threads a few microns wide may total 110 quadrillion kilometres
A hypha is a long, branching thread built by fungi, oomycetes and some actinobacteria, and a mass of them makes a mycelium. Each is only about four to six micrometres wide, yet the hyphae of arbuscular mycorrhizal fungi alone are estimated to add up to roughly 110 quadrillion kilometres.
The name comes from the ancient Greek word for web. A hypha is one or more cells inside a tube-shaped wall, which in fungi is usually stiffened with chitin rather than the cellulose found in plants and oomycetes. Most fungi divide the tube into compartments with cross-walls called septa, but these are normally pierced by pores wide enough for ribosomes, mitochondria and sometimes whole nuclei to drift from one cell to the next. Some groups, such as Mucor, skip the septa entirely, and yeasts make frail pseudohyphae by budding without fully separating.
Growth happens only at the tip. There an organelle called the Spitzenkörper, German for pointed body, gathers vesicles from the Golgi apparatus and ships wall materials and new membrane to the leading edge. Septa form behind the advancing tip, and new branches arise either when a tip forks in two or when a fresh tip sprouts from an older thread. An electric field can steer the direction of growth, hyphae can detect reproductive units some distance away and head for them, and they can thread their way through a permeable surface.
Many are reshaped for particular jobs. Parasitic fungi push absorbing haustoria into host cells, mycorrhizal fungi form arbuscules that trade nutrients and water with plant roots, and nematode-trapping species turn hyphae into snares. Lichens are largely hyphae wrapped around their algal partners.
Mycologists also sort fruiting bodies by hyphal type. Thin-walled generative hyphae occur in every fungus, while thick-walled skeletal and antler-like binding hyphae make polypores leathery or woody. In 1932 E. J. H. Corner called systems with one, two or three types monomitic, dimitic and trimitic, adding further terms in 1966.
Source: Hypha
