Growth characters. – Rate of growth rapid, the radius at 1 week 5.4-5.8 cm. Advancing zone even, hyaline and appressed. Mat white, at first raised, floccose-cottony to floccose-woolly, after 2-5 weeks becoming more compact, floccose-woolly, floccose-felty, woolly-felty to felty, roughly poroid to foliose fruit-bodies formed at some places on the surface of mat or more frequently along the wall of the petri-dish, after 6 weeks mat floccose-felty to felty. Reverse slightly bleached. Odour none.
Tests for extracellular oxidase positive: on gallic acid agar diffusion zones strong to very strong and no growth; on tannic acid agar diffusion zones moderately strong, diameter 3.4 cm; with guaiacum reaction strong.
Hyphal characters. – Advancing zone: hyphae hyaline, thin-walled, nodose-septate, branched, 1.8-4.3 µm in diameter. Aerial mycelium: (a) hyphae as in advancing zone; (b) fibre hyphae numerous, with walls thick and refractive, lutina narrow to apparently lacking, mostly unbranched to sparingly branched or some hyphae very closely branched with manu short branches (cf. to binding hyphae of fruit-body), 1.5-3.0 µm in diameter.
Fruit-body: (a) basidia 4.8 6.0 µm in diameter; (b) basidiospores hyaline, even, cylindric, 4.6 × 1.8-2.0 µm. Submerged mycelium: (a) hyphae as in advancing zone; (b) in old cultures one to two-celled fragments of hyphae present, less common, thin to slightly thick-walled, often swollen and rounded to irregular in chape, appearing like chlamydospores, 3.0-7.4 µm wide.
P. hirsutus has been described in culture by Nobles (1948).
The fungus is very close to P. versicolor. However the culture of P. hirsutus remains white and it forms fruit bodies within 6 weeks whereas the culture of P. versicolor develops creamy to brownish colour in some areas after 2-3 weeks and does not form fruit bodies in 6 weeks. The optimum temperature for growth for P. hirsutus lies between 33 and 36°C and for P. versicolor at 30°C (Sehgal, Sen and Bakshi 1966).
The grey, hirsute upper surface and the greyish pore surface are characteristic of basidiocarps of T. hirsuta. T. versicolor basidiocarps differ in being markedly more adpressed velutinate and zonate, those of T. ochracea and T. pubescens have a tomentose upper surface with a pale margin.
Basidiocarps annual, effused-reflexed or rarely resupinate, coriaceous when fresh; pilei dimidiate, applanate to thick, upper surface hirsute, gray, zonate or concentrically sulcate; margin often yellowish-brown, tomentose; pore surface white to tan or cinereous, the pores (1-)3-4 per mm, with thick, entire dissepiments that become thin with age; context duplex, the upper layer gray, soft-fibrous, up to 3 mm thick, at least at the base separated by a thin black line from the lower part, the latter ivory white, corky, up to 15 mm thick; tube layer concolorous with lower context, up to 6 mm thick.
Hyphal system trimitic; contextual generative hyphae thin-walled, with clamps, 2.5-9 µm in diam; contextual skeletal hyphae thick-walled, often sinuous, hyaline, nonseptate, with rare branching, 3-9 µm in diam; contextual binding hyphae thick-walled, nonseptate, much branched, 2-4 µm in diam; tramal hyphae similar.
Cystidia absent; fusoid cystidioles present, 12-18 × 3-5 pm; hyphal pegs occasionally present.
Basidia clavate, 4-sterigmate, 15-22 × 5-7 µm, with a basal clamp.
Basidiospores cylindric; hyaline, smooth, negative in Melzer’ s reagent, 6-9 × 2-2.5 µm.
Type of rot. White rot of dead hardwoods; positive in gum guaiac solution.
Cultural characteristics. See Nobles, 1948, 1958 and 1965; Bakshi et al. 1969; Stalpers 1978.
Sexuality. Heterothallic and tetrapolar (Nobles et al., 1957), also reported as heterothallic and bipolar (Bose 1934).
Substrata. Dead wood of numerous genera of hardwoods including Abutilon, Acer,
Aesculus, Ahrus, Betula, Castanea, Catalpa, Corylus, Cratageus, Cytisus, Eucalyptus, Fagus, Fraxinus, Gleditschia, Gonzora, Hedera, Juglans, Laurus, Ligustruin, Liriodendron, Males, Morus, Osmanthus, Ostrya, Partenocissus, Populus, Primus, Pyrus, Rhamnus, Rhododendron, Robinia, Rosa, Quercus, Salix, Sorbus, Tilia, Ulmus, Wisteria and numerous other more ornamental bushes. More rarely it has been collected on conifers like Abies, Cupressus, Juniperus, Larix, Picea, Pinus and Taxus. Distribution. Throughout forest regions of Europe and circumpolar in the boreal-temperate zone. North to Finnmark in northern Norway.