Solitary, or in twos or threes, frequently also more or less fasciculate. Growing near the base of the trunks of deciduous trees (often Quercus), and also on the base of the trunks, and on fallen branches or on underground parts of bushes. Summer to autumn. Widely distributed in southern parts of Norway. Also recorded in Troms.

Pileus 20-45 mm across, conical to parabolical or irregularly plano-convex, usually with prominent umbo, sulcate, translucent-striate, pruinose, glabrescent, somewhat lubricous when wet, fairly dark brown, grey-brown to grayish, paler towards the margin, with age sometimes stained with brown spots. Odour indistinctive. Lamellae 23-32 reaching the stipe, tender to somewhat elastic, ascending, narrowly adnate,smooth to somewhat rugulose, dorsally intervenose with age,  white to grey, gradually turning more brownish, sometimes flushed with pink, with age often stained with red-brown spots, the edge concolorous. Stipe 50-80(-180) x 1.5-5 mm, hollow, cartilaginous, straight, equal for the greater part, somewhat widening towards the base, terete or slightly compressed below, strongly and coarsely grooved to smooth, floccose-puberulous above, floccose-fibrillose farther down, glabrescent, silvery grey to slate grey or brownish grey, occasionally brown-spotted, the base densely covered with long, coarse, flexuous, sometimes woolly, white fibrils, usually rooting.

Basidia 27-38 x 8-10 µm, clavate, 4-spored, with sterigmata up to 7.5 µm long. Spores 8-10.5 x 5.2-7.5 µm, Q 1.2-1.6, Qav 1.3-1.4, fairly broadly pip-shaped, smooth, amyloid. Cheilocystidia 19-60 x 5-11 µm, forming a sterile band, fusiform, lageniform, utriform, subcylindrical or irregularly shaped, smooth or with a few coarse, unevenly spaced excrescences, either apically or laterally. Pleurocystidia not observed. Lamellar trama dextrinoid. Hyphae of the pileipellis 1.5-4 µm wide, covered with scattered to crowded excrescences 2-25 x 0.5-1.5 µm, often very densely branched, tending to form dense masses, often embedded in gelatinous matter, and difficult to see clearly. Hyphae of the cortical layer of the stipe 2-4.5 µm wide, smooth or covered with a few scattered excrescences, the terminal cells 3.5-9 µm wide, forked or branched or apically coiled, generally with a few coarse excrescences up to 13.5 x 5.5 µm. Clamp connections abundant and easy to see.

Mycena polygramma can usually be identified on account of the large size, a brownish to brownish grey pileus and the longitudinally grooved stipe. Sometimes the stipe is strikingly sulcate, but still it is not always a reliable differential feature. The stipe is not always very distinctly grooved and sometimes it may be entirely smooth, although the striae often will be visible at the apex. Another species that may cause confusion is M. vitilis (Fr.) Quél. It is usually a smaller species but combines the same colours as M. polygramma. They can be told apart as follows:

Because it sometimes developes brown spots on cap and stipe, it can be confused with with Mycena maculata. I have in fact seen several collections of M. polygramma misidentified as M. maculata. They can easily be distinguished in the microscope.

Several forms and varieties have been described of this species. Sometimes small growth-forms can be found on moss covered oak trunks, and these have been described as var. nana Killerm. and f. pumila J.E. Lange. White forms can also rarely be encountered and are described as Mycena polygramma f. candida J.E. Lange. Robich (2010: 9) proposed a new form based on material with entirely smooth stipes and named it f. laevipes. Such specimens are not unusual and intermediate forms exist, so in my opinion a formal description seems somewhat unnecessary.