Entoloma atromadidum  

A “big blue pinkgill” (Entoloma bloxamii sensu lato), with very dark navy cap and stipe colouration, often radially grooved or slightly wrinkled margin, and small pentagonal to hexaonal spores (max spore length less than 8.5 µm, average around 7 µm).

Pileus (cap) up to 75 mm diam., tricholomatoid (mushroom with notched gill attachment, a thick fleshy stem and lacking a ring or volva), convex to umbonate (with raised central bump or “umbo”), margin initially incurved becoming wavy, irregular and split, indigo to dark greyish blue sometimes with violaceous tones, initially tacky becoming dry and matt and often developing a fibrillose (fibrous), radially grooved or rivulose (marked with irregular, narrow, sinuous, or crooked lines) texture especially towards the margin. Lamellae (gills) sinuate (can sometimes appear free), initially white/whitish with slight bluish tones especially near pileal margin where lamellar edge may also be blue, becoming entirely pink as spores mature, with entire, uneven or serrulate fertile margin. Stipe (stalk) up to 55 x 15 mm, cylindrical or basally tapered, concolorous with pileus or slightly paler, coarsely fibrillose forming a streaky or semi-reticulate pattern in places, white or dirty yellowish at base. Flesh whitish sometimes mottled with streaks of pileal colour. Smell mealy. Spores (from prints or gentle lamellar scraping), measured in 10% ammonia following Noordeloos (1992) 6.2–8.3 x 6.4–8.0 µm, per-basidioma mean values (n=7) in the range 6.7–7.7 x 6.8–7.4 µm, usually pentagonal to hexagonal in profile, isodiametric to subisodiametric, Q = 0.9–1.1, pink, no Melzer’s reaction. Mature basidia predominantly 4-spored with relatively short sterigmata, abruptly clavate, 28.8–50.0 x 8.8–11.2 µm excluding sterigmatal length (3.0–4.0 µm). Clamp connections at basidial bases and on all other hyphae. Pileipellis (upper skin of cap) an ixocutis (hyphae gelatinous, horizontal, and lying flat) of thin-walled narrow filamentous hyphae 2–5 µm wide overlying a layer of inflated elements to 55 x 40 µm.

Description adapted from Ainsworth et al. 2018. (2018) Big Blue Pinkgills formerly known as Entoloma bloxamii in Britain: E. bloxamii s. str., E. madidum, E. ochreoprunuloides forma hyacinthinum and E. atromadidum sp. nov. Field Mycology 19(1), 5-15.