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Page number:208 
Remarks (public):C. borealis is recognized readily in the field because of the watery and sappy basidiocarps often occurring in abundance, the whitish to pale ochraceous color, the coarsely hirsute pileus, and the slightly irregular pores. Microscopically, the ventricose cystidia are diagnostic. 
Description type:Non-original description 
Description:Climacocystis borealis (Fr.) Kotl. & Pouz. - Ceska Mykol. 12:103, 1958 - Polyporus borealis Fr.. Syst. Mycol. 1:366. 1821.
Basidiocarps annual, often developing in large numbers, pilei fanshaped to broadly sessile, flat and semi-circular, up to 15 cm long, 8 cm wide and 4 cm thick towards the base, often imbricate, soft and watery when fresh. light and brittle when dry. taste mild; upper surface flat to slightly convex. tomentose to hirsute when fresh. but the hairs agglutinate in drying and the surface then often partly glabrous, partly tufted with short stiff hairs, pileus when dry often with radial striae. white to light cream or straw-colored when fresh, deep straw-colored when dry; pore surface white to cream or light straw-colored, usually somewhat oblique, pores thin-walled and angular, in parts more irregular and split, about 1-2 per mm; context white to cream, duplex, with a lower dense layer, up to 2 cm thick; tube layer concolorous with pore surface, up to 5 mm thick. Hyphal system monomitic; contextual generative hyphae with clamps, thin- to thick-walled, moderately branched. up to 8 µm in diam; some long thick-walled segments without clamps resemble skeletal hyphae; tramal hyphae similar, in the subhymenium up to 4 µm wide in diam.
Cystidia usually numerous, ventricose, tapering to the tip, either acute or slightly rounded, mostly smooth. but also some with a few apical grainy crystals, thin-walled in the lower part, distinctly thickened towards the apex. up to 50 µm long from the basal clamps from which they arise, 5-12 µm in diam. embedded in the hymen it, m or slightly projecting.
Basidia clavate, 4-sterigmate, 20-30 x 6-8 µm, with a basal clamp.
Basidiospores broadly ellipsoid. hyaline. thin-walled, smooth. negative in Melzer's reagent, 4.5-6.5 x 3-4.5 µm.
Type of rot. Causes a white mottled rot in the butt and roots of living conifers and continues decay in dead trees and stumps.
Cultural characteristics. See Nobles 1948, 1965; Stalpers 1978.
Sexuality. Heterothallic and tetrapolar (Robak 1932).
Substrata. In Europe known almost exclusively from conifers like Abies, Larix, Picea and Pinus, very rarely on hardwoods like Fraxinus. In North America also noted from Pseudotsuga and Tsuga and rarely on hardwoods like Fagus, Acer. Populus and Quercus.
Distribution. Circumboreal, in North Europe following Picea both in natural stands and plantations, in the Central European mountains known west to eastern France.
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