Entoloma tjallingiorum is a relatively stout member of section Leptonia, characterized by its relatively dark pileus, blue stipe and strongly fibrillose-squamulose covering of pileus and stipe. In western and central Europe it is usually found in association with Quercus, but in northern Europe frequently also on wood of Betula. The rather thin-walled, small spores with blunt angled distinguish it from the closely related taxa Entoloma dichroum and E. allochroum.
Pileus 20-80 mm broad, conical or hemispherical then convex or applanate, usually with low, brown umbo, rarely depressed, with involute then deflexed margin, with undulating marginal zone with age, not hygrophanous, not translucently striate, dark grey-brown, sometimes with blue-violaceous tinges, especially near margin and when young, radially fibrillose, tomentose then squamulose all over, dull. Lamellae, L = 20-40, l = 1-5, moderately distant, segmentiform then ventricose, sometimes thick, sometimes transvenose, white or sordid then sordid pink, rarely with bluish tinge when young, with irregularly serrate, concolorous edge. Stipe 25-110 × 2-12 mm, cylindrical, often broadened towards base, dark blue, blue-grey or grey-violaceous, entirely covered with dark blue fibrils forming minute
squamules or tufts of hairs, especially in upper part, base white or cream-coloured, tomentose. Context concolorous with surface in cortex, pallid in inner part of fleshy specimens. Smell none. Taste mild or somewhat bitter.
Spores 9-11 (-11.5) x 6-7 µm, Q = 1.2-1.4, irregularly 6-9 angled in side-view with rather blunt angled and relatively thin-walled, slightly cyanophilous. Basidia 4-spored, clamped. Lamella edge heterogeneous. Cheilocystidia 20-60 × 6-15 µm, cylindrical- flexuose to slenderly lageniform, thin- or slightly thick-walled, colourless or with brownish walls. Pileipellis a cutis with transitions to a trichoderm, made up of septate, cylindrical to inflated, septate hyphae, 7-20 µm wide with inflated terminal elements, 20-90 × 5-30 µm. Pigment brown, intracellular in pileipellis and in addition also encrusting some of the hyphae of lower pileipellis and upper pileitrama. Clamps abundant.
Habitat: Solitary or in groups on rotten wood of Quercus and Betula in deciduous forest; summer-autumn.
Distribution: rare but wide-spread all over Europe.