Mycelial cords are linear aggregations of parallel-oriented . The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant , and also frequently have similar functions; hence they are also called rhizomorphs (literally, "root-forms"). As well as growing underground or on the surface of trees and other plants, some fungi make mycelial cords which hang in the air from vegetation.[
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Mycelial cords are capable of conducting nutrients over long distances. For instance, they can transfer nutrients to a developing fruiting body, or enable wood-rotting fungi to grow through soil from an established food base in search of new food sources. For parasitic fungi, they can help spread infection by growing from established clusters to uninfected parts. The cords of some wood-rotting fungi (like Serpula lacrymans) may be capable of penetrating masonry.
The mechanism of the cord formation is not yet precisely understood. Mathematical models suggest that some fields or of signalling chemicals, parallel to the cord axis, may be involved.
Rhizomorphs can grow up to in length and in diameter.
Rhizomorph
Rhizomorphs are a special morphological adaptation root-like structures found in fungi. These root-like structures are composed of parallel-oriented Hypha that can be found in several species of wood-decay and Ectomycorrhiza Basidiomycota as well as Ascomycota Fungus.
Known for their role in facilitating the spread and colonization of fungi in the environment, rhizomorphs are the most complex organs produced by fungi. They are made up of highly specialized hyphae that are different in size, orientation, and function.
Rhizomorphs are sometimes called mycelial cords, although they are structurally different: mycelial cords are less complex and have a loose network of Hypha giving an appearance of a fan-like mat,
Development and morphology
The development of rhizomorphs begins with a submerged thallus that produces mycelium (hyphae biomass) that when deprived of nutrients and exposed to increasing oxygen, morphogenesis occurs giving rise to pseudo or microsclerotia (survival structures of some fungi), which precede rhizomorph development.
Rhizomorphs contain four differentiated types of tissues:
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The outer layers are a compact growing point that make up the mucilage
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The Melanin wall that serves as protection against colonization by another microorganisms (bacteria or fungi)
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The medulla that serves for conduction of water and dissolved nutrients
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The central line used as an air conducting channel.
Rhizomorphs can be of a cylindrical or flat type, and melanized or unmelanized, respectively.
Function
Rhizomorphs act as a system of underground absorption and growth structures that invade and decay roots and wood,[ They can access places where food resources are not available,]
Example taxa
Evolution of rhizomorphs in Armillaria species
The genus Armillaria is a well-studied and widely distributed mushroom-forming genus with rhizomorph production abundant in most species. One of the more common morphological characteristics for the genus is the presence of an annulus, which is a ring-like structure in the stem of the fruiting body with exception of the species Desarmillaria tabescens.
Rhizomorph traits can be found in all species of the Armillaria as well as other fungi but it appears that the most recently diverged species are adapted to form melanized rhizomorphs. Melanin in rhizomorphs are known for the absorption of metal ions from the soil and can be found in different structures such as and cell walls of fungi among others. Functions of melanin also include protecting against UV radiation and moisture stress.
Aerial rhizomorphs in the Marasmiaceae
Brunneocorticium is a fungus known only from its branched white aerial rhizomorphs which grow in tropical forest canopies. DNA analysis has shown it to belong in the Marasmiaceae (normally a mushroom-forming family), but no fruiting bodies or other fertile structures of it have been found.[
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Marasmius crinis-equi ("Horse-hair fungus") is another species which generates aerial rhizomorphs, but these often have tiny mushrooms branching out from them.
