Marasmiellus

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.[3][4] 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.[5]

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.[6] Observations of rhizomorph-forming species of Marasmiellus have also been confirmed (e.g Marasmiellus tenerrimus var setulosu and Marasmiellus opacu).[7]

Marasmiellus candidus (Bolton) Singer

Marasmiellus only represented three species when it was first described by William Murrill (Marasmiellus inconspicuous Murrill (Cuba), Marasmiellus purpureus (Berk. & 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.[4] Marasmiellus was traditionally included in Tricholomataceae R. Heim ex Pouzar,[8] 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.[9][4] 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.[10][9]

• List of Marasmiaceae genera