Genus of fungi
Marasmiellus is a genus of fungi in the family Omphalotaceae. The widespread genus, circumscribed by American mycologist William Murrill in 1915, contains over 250 species. The name comes from the Greek "marasmus" meaning "wasting".
Morphology and life cycle.
The morphology of "Marasmiellus" has received little attention compared to other genera of "Omphalotaceae", mainly due to their uncolorful pileus, small basidiocarps, and little variation in morphological characters. These factors complicate delimitations of species within this genus. Species of "Marasmiellus" have prostrate and diverticulate hyphae, which have no clear orientation. However, it has been observed that other hyphae can aggregate in fascicles and be radially oriented. Furthermore, cheilocystidia arise from horizontal hyphae and are frequently embedded in the hymenium, often being prostrate. Some species of "Marasmiellus" use basidiospore germination, and distinguishing different genera based on reproduction would depend on the speed of germination. During germination spores of Marasmiellus tend to disperse in dilution platings. Some species are tetrapolar. Additionally, no bipolar or amphithallic taxa in this genus have been reported, which is unexpected, as this mating behavior is common for tropical agarics, by allowing rapid colonizations. Their basidiocarps are collybioid or omphalioid and they have a white spore print. The cutis consis of a pileipellis, which sometimes transitions into a trichoderm, either with or without Rameales-structure.
Ecology.
Species of "Marasmiellus" are distributed around tropical and sub-tropical forested areas around the world, where they play a significant ecological role by being saprotrophic, degrading leafy and woody remains. Some species are parasitic and attack certain plants that are economically important, such as sugar cane, maize, bananas, and coconut palms. Observations of rhizomorph-forming species of "Marasmiellus" have also been confirmed (e.g "Marasmiellus tenerrimus" var "setulosu" and "Marasmiellus opacu").
Taxonomy.
"Marasmiellus" only represented three species when it was first described by William Murrill ("Marasmiellus inconspicuous" Murrill (Cuba), "Marasmiellus purpureus" (Berk. &amp; Curt.) Murrill (Cuba), and "Marasmiellus juniperinus" Murrill (Jamaica)). Currently the genera consists of more than 250 species, of which the type species, "M. juniperinus," remains the same as when the genera was first described. "Marasmiellus" was traditionally included in "Tricholomataceae" R. Heim ex Pouzar, but later DNA studies showed that parts of the genus belong to Omphalotaceae"," which was described by A. Bresinsky in 1985. Furthermore, several studies show that the "Marasmiellus" branched as multiple polyphyletic and artificial groups"." This has led to conflict surrounding its position relative to "Gymnopus", and has resulted in two opposing views regarding their taxonomy: 1) "Marasmiellus" is encompassed within "Gymnopus" (inclusive), or 2) "Marasmiellus" remains a distinct genus from "Gymnopus" (restrictive). The most recent studies have shown that the second hypothesis is the strongest, placing "Marasmiellus" as a separate genus, but more research is required to confirm this.
Species.
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References.
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