In true

slime mold Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myxogastria ...

s (

myxogastria Myxogastria/Myxogastrea (myxogastrids, ICZN) or Myxomycetes ( ICN) is a class of slime molds that contains 5 orders, 14 families, 62 genera, and 888 species. They are colloquially known as the ''plasmodial'' or ''acellula ...

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

s, and in species of the family

Clavicipitaceae The Clavicipitaceae are a family (biology), family of fungi within the order Hypocreales. A 2008 estimate placed 43 genus, genera in the family, but a study in 2020 has increased this number to 50. Phylogeny Molecular phylogeny, phylogenetic ana ...

, the hypothallus is the layer on which the fruit body sits, lying in contact with the substrate. The word is derived from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

root ''hypó'' ("under") and ''thallós'' ("shoot" or "

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

"). The hypothallus is produced by the

plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a Hematophagy, blood-feeding insect host (biology), host which then inj ...

at the beginning of fructification. Depending on the species, it can be membranous to thick or tender to solid and nearly transparent to brightly coloured. It may surround an individual fruit body, or may form a contiguous connection between multiple fruit bodies. In some rare cases it is missing entirely. In

crustose lichen Crustose lichens are lichens that form a crust which strongly adheres to the Substrate (biology), substrate (soil, rock, tree bark, etc.), making separation from the substrate impossible without destruction. The basic structure of crustose lichen ...

s, the hypothallus is the blackish lower layer of the thallus that produces

rhizine In lichens, rhizines are multicellular root-like structures arising mainly from the lower surface. A lichen with rhizines is termed rhizinate, while a lichen lacking rhizines is termed erhizinate. Rhizines serve only to anchor the lichen to their s ...

s, which are holdfasts that attach the lichen to its

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. In some

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

the hypothallus may be involved in the formation of the fruit body. In the "epihypothallic" Stemonitida, the hypothallus forms hollow, tubular stems and a

columella Lucius Junius Moderatus Columella (, Arabic: ) was a prominent Roman writer on agriculture in the Roman Empire. His in twelve volumes has been completely preserved and forms an important source on Roman agriculture and ancient Roman cuisin ...

, up which the remaining plasmodium then rises, producing the

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s. In all other myxogastria "subhypothallic" development takes place. Here, the hypothallus produces a layer on the plasmodium, which creates the rooms of the single fruit bodies during fructification. As the surrounding plasmodium flows in the fruit body, the hypothallus will lie directly on the substrate, shrinking and creating the edge of the mature fruit body. Here, the hypothallus is part of a morphological unit with peridium and stem, which serves as a membranous surface of the whole structure with the spores. Epihypothaly is an

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a Synapomorphy, derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or Outgroup (cladistics), outgroup taxa, not ...

of the stemonitida and is, in comparison to subhypothaly, a primitive feature.

References

{{Reflist, colwidth=30em, , refs= Reference for the paragraph: Henry Stempen, Steven L. Stevenson: Myxomycetes. A Handbook of Slime Molds. Timber Press, 1994, {{ISBN, 0-88192-439-3, p. 26. A.-M. Fiore-Donno, C. Berney, J. Pawlowski, S.L. Baldauf: ''Higher-Order Phylogeny of Plasmodial Slime Molds (Myxogastria) Based on Elongation Factor 1-A and Small Subunit rRNA Gene Sequences.'' In: Journal of Eukaryotic Microbiology, 52, pp. 201–210, 2005 Reference for the paragraph: A.-M. Fiore-Donno, C. Berney, J. Pawlowski, S.L. Baldauf: ''Higher-Order Phylogeny of Plasmodial Slime Molds (Myxogastria) Based on Elongation Factor 1-A and Small Subunit rRNA Gene Sequences.'' In: Journal of Eukaryotic Microbiology, 52, pp. 201–210, 2005 Reference for the paragraph: Wolfgang Nowotny: ''Myxomyceten (Schleimpilze) und Mycetozoa (Pilztiere) - Lebensformen zwischen Tier und Pflanze'' In: {{ISBN, 3854740565, pp. 7–37. Wolfgang Nowotny: ''Myxomyceten (Schleimpilze) und Mycetozoa (Pilztiere) - Lebensformen zwischen Tier und Pflanze'' In: {{ISBN, 3854740565, pp. 7–37. {{cite book , author1=Ulloa, Miguel , author2=Halin, Richard T. , title=Illustrated Dictionary of Mycology , edition=2nd , year=2012 , publisher=The American Phytopathological Society , location=St. Paul, Minnesota , isbn=978-0-89054-400-6 , page=296 Fungal morphology and anatomy Cell biology