Table 2.

Morphological comparison of Mycenacaeruleogrisea, M.caeruleomarginata, and related species.

Taxa	M.caeruleogrisea	M.caeruleomarginata	M.subcaerulea	M.amicta	M.cyanorhiza	M.interrupta
Pileus	12–25 mm diam., hemispherical when young, conical, obtusely conical, campanulate with age, smooth when young, becoming slightly brownish scaly at the center, pruinose, acid blue to dull blue at the center and margin pallescent, turning bluish gray, covered by a separable, gelatinous pellicle.	3.5–13 mm in diam., parabolic, obtusely conical when young, hemispherical, campanulate with age, with an umbo at the center, shallowly sulcate, translucent-striate, smooth, gelatinous slightly, the margin infrequently out of flatness, brown to dark brown, becoming acid blue to dull blue towards the margin, with a greyish white margin, covered by a separable, sticky pellicle.	(3)5–15(25) mm broad, more or less ovoid with an appressed or slightly incurved margin, becoming obtusely conic to campanulate, surface lubricous subviscid, glabrous or appearing somewhat granulose near the margin, translucent-striate, pellicle tenacious and completely separable, pale blue or greenish blue, soon tinged with brown and assuming various degrees of bluish, greenish, or grayish brown with a pallid margin, often sordid yellowish in age, bluish tints often lingering on the margin.	5–15 mm wide, conical to campanulate, ± sulcate, translucent-striate, finely puberulous, covered with a separable gelatinous pellicle, pale grey-brown or pale sepia brown, sometimes with an olivaceous, greenish or bluish green shade, margin often bluish green, or more rarely dingy citrine to ochraceous yellow.	2–5(–10) mm wide, covered with a (separable), gelatinous pellicle, at first ± globose, then hemispherical to parabolic, becoming convex or somewhat depressed, but also with a small papilla, sulcate, translucent-striate, pruinose, glabrescent, somewhat lubricous, initially pale brown, then pale grey with darked centre, becoming almost white with age.	16 mm in diam., up to 4 mm high, at first subglobose to ovoid-conical, with age becoming convex to shallowly so, slightly depressed at apex, shiny, gelatinous, minutely radially rugulose, ± pruinose in places, at first dull blue at apex, below apex, becoming dull blue towards margin; margin decurved, entire, sulcate, striate, faintly translucent-striate.
Context	White, thin, fragile.	White, fragile, thin.	Thin, pallid, pliant.	–	–	Very thin to moderately thick at apex, translucent white or translucent greyish white.
Lamellae	16–28 reaching the stem, adnate to slightly adnexed with a short tooth, narrowly spaced, white, with intervenose veins.	14–25 reaching the stem, adnate to slightly adnexed with a short tooth, white, with unconspicuous intervenose veins, edges concolorous with the face.	Close to crowded, 18–25 reach the stipe, two or three tiers of lamellulae, ascending-adnate, sometimes narrowly adnate or practically free, narrow to moderately broad, white or tinged grayish, edges slightly fimbriate.	17–25 reaching the stem, ascending, adnexed, greyish to greyish brown; edge whitish, at times yellowish, greenish or bluish near the cap margin.	9–14 reaching the stem, ascending, adnexed to fairly broadly adnate or almost free, sometimes with a pseudocollarium, whitish or pale grey; edge whitish and separable as an elastic-tough thread.	Free from stipe or adnately attached to obvious circular descent of pileal flesh, moderately close to distant, five to seven per quadrant, subventricose, moderately broad to broad; edge marginate, blue; sides minutely pruinose, white; with one or two series of lamellulae.
Stipe	48–76 × 1.5–2.0 mm, equal or slightly broadened below, hollow, fragile, pruinose, white, base acid blue in the whole age, covered with white fibrils.	32–46 × 1.0–2.0 mm, equal, base sometimes slightly broaden, fragile, hollow, pruinose, puberulous entirely when young, becoming sparely especially in the middle part when old, yellowish brown to light brown, base with acid blue tinge, covered with a bit white fibrils.	3–8 cm long, 1–2 (2.5) mm. thick, equal, terete, flexuous or strict, tubular, cartilaginous, elastic, at first densely pruinose or minutely pubescent over all form a dense coating of caulocystidia, somewhat glabrescent, base mycelioid, the mycelium blue at first but soon fading to white, bluish to greenish blue above at first, soon fading to grayish or finally sordid brownish.	40–70 × 0.5–2 mm, cylindrical, entirely covered with a dense and fairly coarse, white pubescence, greyish brown, usually somewhat paler at the apex, occasionally with a slight lilaceous or violaceous tint; base at times somewhat rooting, concolorous or with some blue-green stains or entirely blue, even the substrate may be stained blue.	5–30 (–70) × 0.5–1 mm, cylindrical, entirely puberulous, glabrescent in the middle part, pale grey to hyaline-white; base hirsute, sky blue (also in the flesh), springing from a patch of fine, radiating, white fibrils.	Up to 22 mm long, cylindrical, moist to dry, often pruinose especially towards base, translucent white, attached to substratum via white pruinose disc borne on a flattened dull blue base.
Odor & taste	Indistinctive	Indistinctive	Mild	Indistinct to raphanoid.	Smell none or reported as faintly nitrous; taste not recorded.	Odour not distinctive.
Spores	(9.0) 9.3–11.6 (11.8) × (6.0) 6.2–7.3 (7.7) μm, Q = 1.5–1.7, ellipsoid, amyloid.	(6.2) 6.4–7.7 (7.9) × (4.4) 4.7–5.8 (6.0) μm, Q = 1.23–1.54, broadly ellipsoid to ellipsoid, amyloid.	6–8 × 6–7 (8) μm, globose or subglobose, amyloid.	7.5–10.7 × 4.5–6 μm, Q = 1.5–1.9, Qav ≈ 1.6, pip-shaped, amyloid.	6.5–9 × 4–5 μm, Q = 1.6–2.2, Qav ≈ 1.8, pip-shaped, amyloid.	(54/3), 8.4–11.6 (x̄ = 9.9, SD = ± 0.7) × 5.7–8.8 (x̄ = 7.0, SD = ± 0.6) μm, Q = 1.4, broadly ellipsoidal rarely subglobose, with prominent short, oblique apiculus, amyloid.
Basidia	22–29 × 7–9 μm, 4- or 2-spored.	26–35 × 6–12 μm, 4- or 2-spored.	4-spored	30–40 × 6–7 μm, clavate, 4-spored.	18–25 × 6.5–11 μm, clavate, 4-spored.	(27/2), 21.6–39.8 (x̄ = 29.0, SD = ± 5.2) × 8.3–16.0 (x̄ = 11.6, SD = ± 2.6) μm, 4-spored, rarely 2-spored, sterigmata to 8.8 μm long.
Cheilocystidia	40–62 × 4–6 μm, clustered, abundant, long clavate or cylindrical, apically broadly rounded, thin-walled, hyaline, forming a sterile lamellae edge.	32–48 × 4–6 μm, abundant, clustered, cylindrical or long clavate, apically broadly rounded, thin-walled, hyaline, forming a sterile lamellae edge.	Abundant, 32–60 × 5–8 μm, subfusoid with obtuse apices but becoming more or less cylindric, sometimes flexuous, smooth, hyaline.	16–45 × 3.5–7 μm, clavate, subfusiform or more often cylindrical.	9–20 × 5.5–7 μm, embedded in gelatinous matter, clavate to obpyriform, with few, simple to branched excrescences, 3–14 × 1–1.5 μm.	Abundant, (30/1), 16.8–44.8 (x̄ = 25.5, SD = ± 6.55) × 5.6–13.6 (x̄ = 8.4, SD = ± 1.8) μm, filamentous, cylindrical, clavate to ovoid, sometimes ventricose at base, with nodulose excrescences.
Pleurocystidia	Absent	Absent	Not differentiated	Absent	Absent	Absent
Pileipellis	Hyphae 1–4 μm wide, sparse, smooth or sparsely coated with simple, cylindrical excrescences or inflated cells, 3.1–11.2 × 0.8–1.7 μm, embedded in gelatinous matter.	Hyphae 2–4 μm wide, with simple, cylindrical excrescences, 2.0–6.4 × 0.6–1.8 μm, embedded in gelatinous matter.	A thick gelatinous pellicle (blue color located along the surface of the pellicle in incompletely gelatinized hyphae).	Hyphae 2–4.5 μm wide, branched, anastomosing, smooth with scattered, cylindrical excrescences, embedded in a layer of gelatinous matter.	Hyphae 1.5–3.5 μm wide, embedded in gelatinous matter, very branched, covered with scattered, simple to branched excrescences, protruding through the gelatinous layer.	Hyphae (28/1), 2.8–8.0 (x̄ = 5.4, SD = ± 1.4) μm in diam., nodulose-diverticulate with dense nodulose to cylindrical excrescences, gelatinized.
Stipitipellis	Hyphae 3–8 μm in diameter, smooth, hyaline.	Hyphae 3–6 μm in diameter, smooth, hyaline.	–	Hyphae 2–3.5 μm wide, smooth	Hyphae 1–3 μm wide, smooth.	Hyphae (26/1), 1.6–3.2 (x̄ = 2.4, SD = ± 0.4) μm in diam., not gelatinized.
Caulocystidia	38–69 × 6–8 μm, long cylindrical, smooth, transparent.	19–40 × 4–8 μm, smooth, transparent, two shapes: fusiform or cylindrical.	Covered with numerous cystidia, elongated and flexuous.	50–145 × 8–11.5 μm, fusiform to subcylindrical.	Up to 60 × 7 μm, simple to furcate or somewhat branched.	Often fasciculate, (25/1), 50.6–128.0 (x̄ = 75.0, SD = ± 19.8) × 5.0–8.8 (x̄ = 6.3, SD = ± 1.1) μm, filamentous to slightly ventricose especially towards base, rarely bifurcate.
Clamps	Present	Present	Present	Present	Present	Present
Habitat	Scattered, on humus and fallen leaves in Acer, Populus, Pinus, and Quercus mixed forests.	Scattered, on rotten wood in Picea, Pinus, Quercus, Robinia, and Tilia mixed forests.	Single, scattered or gregarious on debris, decaying wood, or on the bark around the bases of live trees of oak in particular, but also occurring quite frequently on decaying wood of basswood, elm, beech, and other hardwoods.	On wood and woody debris, mostly from conifers but also deciduous trees, also among leaves and needles.	On conifers (Picea, Pinus and Larix) bark and twigs, often on small bark fragments deep in grass.	Generally gregarious, often abundant, rarely solitary or scattered, on fallen decayed logs or stumps of Eucalyptus, Nothofagus, Bedfordia, Pinus, etc. forest.
Distribution	China	China	North America (Alabama, Carolina, New York, Tennessee, Pennsylvania, Michigan); Canada (Nova Scotia, Ontario, Manitoba)	Europe (Scandinavia, Netherlands, Italy)	Europe (UK, Denmark, Italy)	Australia and New Zealand
Occurrence time	Summer to autumn.	Late summer to early autumn.	Spring to fall, more abundant locally in the spring.	Late summer to late autumn, rarely in spring.	Summer to autumn.	March to July.
References	This study	This study	Saccardo 1887; Smith 1947	Robich 2003; Aronsen and Læssøe 2016	Robich 2003; Aronsen and Læssøe 2016; Perry 2020	Grgurinovic 2003