Exidia pithya Fr.
Abstract
Exidia pithya Fr., Systema Mycologicum 2: 226, 1822 Figs 19 G, 19 H, 20 E, 20 F = Tremella nigricans With., A Botanical Arrangement of All the Vegetables, Naturally Growing in Great Britain 2: 732, 1776. = Exidia nigricans (With.) P. Roberts, Mycotaxon 109: 220, 2009. = Exidia plana Donk, Persoonia 4: 228, 1966. Neotype (designated here, MBT 10031436). Sweden • Bohuslän: Hönö, Ersdalsvägen, Pinus sylvestris (fallen corticated log), 12 Aug 2024 Spirin 17359 * (GB) (Figs 19 G, 19 H, 20 E, 20 F). Description. Basidiomata annual, at first cushion- or button-shaped, then adpressed-orbicular or more rarely nearly cerebriform, up to 5 cm in diam., broadly attached, in large groups, finally often fusing together and reaching 30 cm in the longest dimension, up to 1.5 cm thick, gelatinous. Hymenial surface uneven or variably folded, as a rule covered by rather regularly arranged spike-like black projections up to 0.2 mm long, at first gray to brownish-gray, later brownish-black, in older basidiomata sometimes fading to yellowish-brown, in dry condition completely black. Abhymenial surface smooth or near so, concolourous with or slightly paler than hymenial surface. Margin free, concolourous with hymenial surface, entire, even or lobate. Hyphal structure monomitic, hyphae clamped; context hyphae hyaline to grayish, occasionally encrusted by brownish deposits, thin- to slightly thick-walled, interwoven or subparallel, anastomosing, 0.5–6 μm in diam., subhymenial hyphae hyaline to grayish or brownish, thin-walled or with a distinct wall, ascending or interwoven, 1–3.5 μm in diam., occasionally irregularly inflated (up to 7.5 μm in diam.), basidia-bearing hyphae 2–5.5 μm in diam. Hyphidia with a brownish, occasionally irregularly inflated hyphoid stem, 2–10.5 μm in diam., and hyaline or brownish apical branches, 0.5–1 μm in diam., forming a continuous layer up to 50 μm thick. Probasidia bullet-shaped or broadly clavate, 10.5–23 × 4–10 μm. Basidia four-celled, ellipsoid-ovoid, (10 –) 11.5–20.5 (– 21.5) × (7.9 –) 8.1–11.8 (– 12.1) μm (n = 160 / 14), sterigmata up to 25 × 1–2.5 μm. Basidiospores narrowly to broadly cylindrical, more rarely allantoid, slightly or moderately curved, (8.1 –) 8.3–16.7 (– 19.7) × (3.1 –) 3.2–5.2 (– 5.3) μm (n = 560 / 19), L = 9.55–14.43, W = 3.59–4.61, Q = 2.49–3.49. Remarks. As redefined here, E. pithya is morphologically most similar to E. friesiana. Both species produce black or nearly black, adpressed-orbicular basidiomata with smooth abhymenial surface, soon fusing together and making up compound, irregularly shaped fructifications. The main macroscopic differences between the two species are a more distinctly folded hymenial surface of E. pithya compared to E. friesiana and the presence of sharp or blunt hymenial projections in the first species. Microscopically, E. pithya differs from E. friesiana in having more irregularly arranged subhymenial hyphae (often partly ascending and partly interwoven in the same fruitbody) and narrower and as a rule shorter basidiospores. Additionally, E. pithya occurs on both angiosperms and conifers, while E. friesiana is restricted to freshly fallen logs and branches of Abies and Picea spp. (as well as Pinus in the Mediterranean). Up to now, E. pithya was believed to be a conifer-dwelling species which was differentiated from the similar E. glandulosa sensu Neuhoff (= E. nigricans after Roberts 2009) by its host preference. The latter species was described as growing exclusively on deciduous trees (Raitviir 1970; Hansen and Knudsen 1997). However, some authors noted that the so-called E. glandulosa can also be found on conifers (Neuhoff 1936 a; Pilát 1957; Torkelsen 1972; Wojewoda 1981), and that its only reliable trait versus E. pithya is the presence of hymenial outgrowths. This concept, as well as the application of the name E. pithya to the species without these projections came from Neuhoff (1936 a). In our opinion, this viewpoint cannot be maintained because it explicitly contradicts Fries’ description of E. pithya. In his sanctioning treatment, Fries (1822: 226) added the following remark to E. pithya: “ Ad truncos et ramos emortuos pineos, etiam mihi minute papillifera ”. The reference to minutely papillose hymenophore clearly excludes E. pithya in the sense of Neuhoff (= E. friesiana in the present study). Moreover, no verified records of the latter species on Pinus in temperate or boreal Europe are known to us. On the contrary, E. glandulosa sensu Neuhoff (= E. nigricans) occurs in the south-western part of Sweden on both angiosperms and conifers, including pine. We therefore designate one of the sequenced Swedish specimens collected on Pinus as a neotype of E. pithya. Tremella nigricans (= E. nigricans) is an older name for the species reinstated here as E. pithya. However, it has never been sanctioned. Thence, E. pithya has a priority over T. nigricans. Exidia pithya is widely distributed in the northern hemisphere. Its differences from E. friesiana are listed above. However, the boundaries between the two species need further examination. The specimen Burdsall 12029, morphologically matching Exidia pithya and the only North American sample sequenced for more than one marker, shows a conflicting genetic pattern. Its ITS sequence is identical to the European E. pithya whereas its TEF 1 is the same as in E. friesiana. When two unlinked markers fully correspond to organisms from two different species, this usually indicates a very recent introgression event. Other processes, such as incomplete lineage sorting, are less likely – if these markers had been inherited from the ancestral population prior to the species split, enough time should have passed for at least some sequence divergence to accumulate. Denser sampling from North America and additional unlinked markers, ideally supported by mating tests, are needed to clarify this issue. Another widely distributed species similar to E. pithya is E. spiculata. Like E. friesiana, it is totally devoid of the hymenial projections which are characteristic of E. pithya. However, in some collections of E. pithya they can be very sparse or completely lacking, although the number of these deviating specimens is relatively low. See further remarks under E. spiculata.
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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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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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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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
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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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