Exidia impressa Fr.
Abstract
Exidia impressa (Pers.) Fr., Systema Mycologicum 2: 226, 1822 Figs 19 E, 20 C, 22 ≡ Tremella impressa Pers., Mycologia Europaea 1: 102, 1822. Neotype (selected here, MBT 10031435). France. Aveyron: Millau, Le Monna, Laburnum sp. (dead hanging branch), 23 Feb 2025, Spirin 18143 * (H). Description. Basidiomata annual, cupulate-orbicular, up to 3 cm in diam., narrowly attached, up to 0.5 cm thick, gelatinous. Hymenial surface even or indistinctly folded, rarely bearing spine-like outgrowths up to 0.3 mm long, dark reddish-brown to brownish-black, in dry condition completely black. Abhymenial surface rough, covered by tightly arranged dots, brownish-black. Margin free, concolourous with hymenial surface, entire, even or indistinctly lobate. Hyphal structure monomitic, hyphae clamped; context hyphae hyaline or yellowish, with a variably thickened, gelatinized wall, interwoven, anastomosing, occasionally encrusted, 1.5–7 μm in diam., sometimes inflated and then reaching up to 15 μm in diam., subhymenial hyphae hyaline or yellowish, thin-walled or with a distinct wall, predominantly ascending, 1.5–3 μm in diam., basidia-bearing hyphae thin-walled or with a distinct wall, 2–5 μm in diam., often short-celled. Hyphidia of two types: a) hymenial hyphidia, with a hyaline, narrowly clavate or nearly hyphoid stem, 3–5 μm in diam., and predominantly hyaline, usually rather short, dendroid or coralloid apical branches, 1–2 μm in diam.; b) deeply rooted hyphidia, with a hyaline or yellowish-brownish, often encrusted hyphoid stem, 3–8 μm in diam., and yellowish or brownish, usually rather long apical branches, 1–1.5 μm in diam., embedded in yellowish-brownish gelatinous matrix and forming a continuous layer up to 100 μm thick. Probasidia ellipsoid-ovoid, moderately tapering, or clavate, 10–17 × 3–7 μm. Basidia four-celled, narrowly ellipsoid-ovoid or broadly clavate, often obliquely septate, (13.5 –) 15–20 (– 21) × (5.1 –) 5.4–7.3 (– 7.4) μm (n = 20 / 1), sterigmata up to 50 × 1–2 μm. Basidiospores cylindrical to allantoid, slightly or distinctly curved, (8.8 –) 9.0–12.7 (– 13.1) × (3.0 –) 3.1–4.1 (– 4.2) μm (n = 30 / 1), L = 11.01, W = 3.52, Q = 3.16. Remarks. This species was described by Persoon (1822) as Tremella impressa. The protologue referred to another, provisional name, T. rufescens Ehrenb. Fries (1822) sanctioned T. impressa and moved it to Exidia although he had never studied it and simply repeated Persoon’s description. Since then, the identity of E. impressa has remained obscure. Bourdot and Galzin (1927) accepted it as a good species. However, their description seemingly refers to another species, E. straminea (see below). Neuhoff (1936 a) placed E. impressa in the synonyms of E. truncata (= E. glandulosa in the present study), and this synonymy was later accepted by Donk (1966). In our opinion, Neuhoff’s species concept cannot be accepted because it contradicts some important elements mentioned in the protologue of T. impressa. First, Persoon (1822: 102) stated that his species becomes dark reddish-brown in dry condition (“ sicca … rufo fusca fit ”). Further, he specified that it is completely smooth after being rehydrated, and its margin is faintly plicate (“ humectata tota laevis … marginem parum plicata ”, ibid.). All these features clearly rule out E. glandulosa and E. truncata: neither of them show reddish tints, nor is the surface of their basidiomata smooth. Moreover, the basidiome edge of E. glandulosa is clearly folded and sometimes lobate. In E. truncata, as redescribed below, it remains entire and more or less even. The type material of E. impressa is not extant, and we therefore designate a recent, sequenced collection from France as a neotype of T. impressa. In all important aspects, it agrees with the descriptions of Persoon and Fries. Morphologically, E. impressa is strongly reminiscent of species in the E. recisa complex. Due to its dark, opaque basidiomata, it can be easily separated from two other similar species in Europe, E. recisa and E. straminea. These two species have lighter-colored, semitranslucent basidiomata when fresh. Some individuals of E. impressa possess distinct, sharp projections on the hymenial surface. In contrast, the hymenial surface is completely smooth or only indistinctly warted in E. recisa and E. straminea. However, the presence of these outgrowths is inconsistent. In a collection of E. impressa containing multiple basidiomata, some of them may be completely devoid of the hymenial projections. Moreover, hyphidia of E. impressa are of two types – of subhymenial and tramal origin, and they are more or less clearly differentiated from each other. In E. recisa and especially in E. straminea, all kinds of transitions can be found between hymenial and deeply rooted hyphidia. In Asia, E. impressa can be confused with E. yadongensis and E. zelleri. All three species have dark, cupulate-orbicular basidiomata and similar host preferences, and they may occur in the same habitats. Exidia zelleri can be distinguished from E. impressa and E. yadongensis via its large basidiospores and (if sterile) much bigger basidia. Differences between E. impressa and E. yadongensis are discussed under the latter species. We studied and sequenced three collections of E. impressa. They are morphologically very uniform but their ITS sequences show 5–6 bp difference from each other. All these positions are in the ITS 2 region. We preliminarily accept them as a sign of the infraspecific geographic variation. A much denser sampling from different parts of temperate Eurasia is necessary to prove otherwise.
Authors 13
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University of Helsinki · Finnish Museum of Natural History
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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
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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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Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, Netherlands
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Société Linnéenne de Lyon, 33 rue Bossuet, 69006 Lyon, France
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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
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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
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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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