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Remarks (public):For a complete description including images see 
Remarks (internal):Readily distinguished from P. igniarius (CMI Descript. 194) by the bright yellowish context, scanty setae, and larger spores (see also Jacquiot, 1960). The decay caused by P. robustus is slow spreading and does not generally cause extensive damage. It has been reported to be common on oak in France.
Description type:Non-original description 
Description:Phellinus robustus (P. Karst.) Bourd. & Galz., Bull. Soc. mycol. Fr. 41: 188, 1925.
= Fomes robustus P. Karst., Krit. Finl. Basidsv., p. 467, 1889.
Carpophore perennial, solitary, sessile with broad basal attachment, at times resupinate. Pileus 1-16 x 3-25 x 2-15 cm, convex, appressed-reflexed to ungulate; upper surface at first fulvous tomentose, soon greyish-black to black, glabrescent, broadly zoned sulcate, finally rimose but not developing a distinct crust; margin thick, obtuse. Context 1-4 cm thick, bright yellowish-brown, blackening with KOH, silky zonate. Pore-surface yellowish-brown to greyish-brown; pores regular, subcircular, 4-6 (-8) per mm, 10-200 µm diam., dissepiments 35-80 µm thick, edge entire; tubes distinctly stratified up to 20 layers, 4-7 mm long in each layer, paler than context, older layers white stuffed. Basidiospores 6-8 x 5-7 (av. 7 x 6,3) µm, subglobose to globose, hyaline, with a smooth slightly thickened wall and refractive guttulate contents. Basidia 13-17 x 9-11 µm, broadly clavate, 4-spored. Setae present, 20-23 x 8-10 µm, very rare and apparently sometimes absent, pointed, ventricose, occasionally malformed, with a thick chestnut brown wall. Setal-Hyphae absent. Hyphal system dimitic, non-agglutinated, with generative hyphae and skeletal hyphae. Generative Hyphae 1-5 µm diam., hyaline or brownish, usually thin-walled but sometimes thickening, freely branched, simple septate. Skeletal Hyphae 2-6 µm diam., unbranched, of unlimited growth, with a thickened yellowish or reddish-brown wall up to 2,5 µm thick and capillary lumen, non-septate. Colonies growing slowly on malt agar, optimum temperature 26,5-29,5°C, producing 3 mm in 24 hours forming a very tenacious mycelium which may be cut only with difflculty (39: 133); mat felty to woolly, two-zoned with a white marginal zone and a central ochraceous zone with an orange tomentum (40: 255); tests for extracellular oxidase positive (38: 468).
Hosts: Mainly on Quercus, also recorded on Abies, Acacia, Acer, Betula, Buxus, Cassinia, Castanea, Cereus, Eleagnus, Eucalyptus, Fagus, Hippophae, Juglans, Leptospermum, Nothofagus, Opuntia, Picea, Pinus, Pistacia, Pittosporum, Pseudotsuga, Robinia, Salix, Syringa, Taxus, Thuja and Tsuga.
Disease: Yellow trunk rot of oak. A whitish to pale yellowish rot, mainly confined to the sapwood but can also extend to the heartwood, surrounded by a narrow dark brown zone (17: 358). Also causes excrescences on the trunk.
Geographical distribution: Asia (Japan, U.S.S.R.), Australasia & Oceania (Australia, Hawaii, New Zealand); Europe (Czechoslovakia, France, Germany, Great Britain, Hungary, Netherlands, Norway, Spain, Sweden, Switzerland); North America (Canada, U.S.A.).
Physiological specialization: Not known. Jacquiot (1960) found in laboratory tests that deal wood, normally susceptible to attack by wood destroying fungi, was only slowly decomposed when exposed to cultures, which suggested a close adaptation of P. robustus to oak and chestnut, the commonest hosts. Previously, however, Grosjean (25:238) was successful in producing decay in living branches of Quercus and Populus alba using cultures on wood as inoculum.
Transmission: By air-borne spores. Infection occurs through trunk wounds. The perennial carpophore may persist for 15-20 yrs.
Literature: Lohwag, Annls mycol. 35: 339-349, 1937 (decay of oak and chestnut); Davidson & Mielke, Mycologia 39: 210-217, 1947 (heartrot of cacti); Cartwright & Findlay, Decay of timber and its prevention, ed. 2, 1958; Jacquiot, Bull. Soc. mycol. Fr. 76: 83-106, 1960 (cultural characteristics); Pilat, Atlas. des champignons de l'Europe 3: Polyporaceae, p. 504, 1942; Lowe, The Polyporaceae of North America. The genus Fomes, p. 54, 1957 (description).
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