Exidia Fr.
Abstract
Exidia Fr., Systema Mycologicum 2: 220, 1822 = Tremellochaete Raitv., Eesti NSV Teaduste Akadeemia Toimetised 13: 29, 1964. Generic type. Exidia japonica Lloyd. Description. Basidiomata annual, gelatinous, adpressed-orbicular, turbinate or cerebriform, more rarely resupinate and then with adnate, gradually thinning margin, reddish-brown to almost black, more rarely lighter-coloured. Abhymenial surface smooth, dotted, papillose or hirsute; hymenial surface smooth to indistinctly or clearly folded, spine-like projections present in most species. Crystals usually abundant; dark-colored granular incrustation as a rule present on hyphidia and hyphae (apparently lacking in five pale-coloured species). Hyphal structure monomitic; hyphae clamped, in many species encrusted. Cystidia present only in two resupinate species. Hyphidia present, often forming a continuous layer (epihymenial membrane). Basidia four-celled, longitudinally septate, ellipsoid-ovoid or broadly clavate. Basidiospores hyaline, thin-walled, broadly cylindrical to allantoid, usually distinctly curved. On dead wood of angiosperms, more rarely on conifers. Generic type. Tremella glandulosa Bull. Here we reintroduce Exidia for most species previously ascribed to this genus, at least those distributed in Europe. Two other genera encompassing Exidia - like fungi are Descidia and Ulocolla. From them, Exidia s. str. can be distinguished due to two quite distinctive features. First, the majority of Exidia spp. treated below possess spine-like or (in some subtropical / tropical species formerly treated under Tremellochaete) wart-like projections on the hymenial surface. However, these seem to be constantly lacking in a few species of Exidia s. str. Some individuals of the normally papillose species can be devoid of them, too. Additionally, Ulocolla saccharina may sometimes develop clearly visible and rather regularly arranged hymenial projections. In these cases, the genuine Exidia species can be separated from the other exidioid taxa by the permanent presence of the characteristic granular encrustations on hyphidia and, in many cases, also on subhymenial and context hyphae (Figs 21, 22). These discrete deposits are as a rule coloured reddish, brownish or nearly black, and their presence causes the overall basidiome colouration. The incrustation of this type is clearly different from the amorphous yellowish or brownish substance cementing an epihymenial layer in mature basidiomata of Descidia repanda and the exidioid Ulocolla spp. The only two exceptions known to us are Exidia candida and E. semiorbis. In these species, no signs of granular encrustation on hyphidia or hyphae have been detected. Moreover, the epihymenial membrane in E. candida var. candida (= E. villosa) is very loose and it is eventually absent in E. semiorbis. These deviating features make it difficult to differentiate these two species from similar Descidia spp. However, most specimens of E. candida and all known specimens of E. semiorbis bear spine-like projections on their hymenial surface. The basidiospores of E. candida are cylindrical to broadly cylindrical and shorter than in Descidia spp. These two traits help in differentiating E. candida from the superficially similar D. repanda and D. thuretiana. The basidiospores of E. semiorbis are very similar to those of D. repanda. However, mature basidiomata of E. semiorbis are orbicular-cupulate and have a warted abhymenial surface, while they are turbinate or pulvinate and smooth on the outside in D. repanda. The inclusion of four completely resupinate, smooth species in Exidia, i. e. Sebacina plumbescens (= Exidiopsis succinea) and the newly described Exidia delita, E. repleta, and E. saturata, poses another problem – namely, it obfuscates the limits of Exidia vs. the redefined Exidiopsis (E. effusa and E. perflua), Proterochaete (P. abstrusa), Tegmenticium (T. peritrichum) and Ulocolla (U. grisea). The four effused Exidia species can be differentiated from the representatives of the aforementioned genera by their thicker, clearly gelatinous basidiomata and, as a rule, larger basidia. In E. delita and E. plumbescens, the basidiomata usually produce numerous embedded mineral grains easily detectable under magnification. These inclusions are very rare or completely lacking in the similar-looking species of Exidiopsis, Proterochaete, Tegmenticium, or Ulocolla. In turn, E. repleta and E. saturata can be differentiated from the representatives of the four mentioned genera in having thicker epihymenial layer and distinctly inflated hyphae. The identity of the generic type, E. glandulosa, is still a subject of ongoing controversy. We address this issue in remarks to E. glandulosa, E. pithya and E. truncata. In total, 26 Exidia species are described or commented on below and several insufficiently known taxa belonging to the redefined Exidia are addressed in the corresponding section of the paper.
Authors 13
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University of Helsinki · Finnish Museum of Natural History
Affiliation as printed
Finnish Museum of Natural History, University of Helsinki, PO Box 7, 00014 Helsinki, Finland
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Komarov Botanical Institute of the Russian Academy of Sciences
Affiliation as printed
Komarov Botanical Institute, Prof. Popova str. 2, 197022 St. Petersburg, Russia
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Affiliation as printed
Organismic Botany and Mycology, Institute of Plant Science and Microbiology, Ohnhorststraße 18, 22609 Hamburg, Germany
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Affiliation as printed
Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, Netherlands
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Affiliation as printed
Société Linnéenne de Lyon, 33 rue Bossuet, 69006 Lyon, France
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Affiliation as printed
Österplana Skattegården 2, 53384 Hällekis, Sweden
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Affiliation as printed
Globe Institute, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark
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Affiliation as printed
Institute of Biological Sciences, University of Oslo, P. O. Box 1045, Blindern, N- 0316 Oslo, Norway
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University of Tennessee at Knoxville
Affiliation as printed
Department of Ecology and Evolutionary Biology, University of Tennessee, 1406 Circle Drive, Knoxville, Tennessee 37996, USA
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Affiliation as printed
Ecology and Genetics Research Unit, University of Oulu, P. O. Box 3000, FI- 90014 Oulu, Finland
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Czech Academy of Sciences, Biology Centre
Affiliation as printed
Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31, CZ 37005, České Budějovice, Czech Republic
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National University of Misiones
Affiliation as printed
Instituto de Biotecnología Misiones (InBioMis), Facultad de Ciencias Exactas, Químicas y Naturales, Universidad Nacional de Misiones, Ruta Nacional N 12, km 7.5, Posadas, Misiones, CP 3304, Argentina & Instituto Misionero de Biodiversidad (IMiBio), Ruta Nacional N 12, km 5, Puerto Iguazú, Misiones, CP 3370, Argentina
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University of Helsinki · Finnish Museum of Natural History
Affiliation as printed
Finnish Museum of Natural History, University of Helsinki, PO Box 7, 00014 Helsinki, Finland
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