Summary:
Features of Xerocomellus zelleri include 1) a dark vinaceous black, occasionally dark olivaceous black or dark brownish black cap with a paler band around the extreme margin, the surface finely velvety when young, 2) light creamy yellow flesh that sometimes turns slightly blue, 3) moderately sized, round to irregular yellowish pores that occasionally turn blue, 4) a stem with a yellow background that has red punctations at first and becomes more evenly red in its upper part or throughout, 5) growth on or around moss-covered logs in conifer forest, and 6) microscopic characters. Xerocomellus atropurpureus was been included with the species concept of X. zelleri before the description of X. atropurpureus in 2020. The included images specifically represent Xerocomellus zelleri as opposed to X. atropurpureus. Differentiating features between the two are given in the SIMILAR section of Xerocomellus atropurpureus. X. atropurpureus is more common than X. zelleri. Frank(9) say (with Latin names italicized), "Locally common in mature forests on the Olympic Peninsula in Washington, rare across the rest of its range. Despite extensive collecting over a six-year period in [sic], we encountered this species only five times. We studied all observations of X. zelleri on Mushroom Observed (mushroomobserver.org) and concluded that all but one observation from California represent X. atropurpureus."
Xerocomellus zelleri ranges from southern BC to the northern California coast (Frank). Collections were examined from WA, OR, and CA, with additional GenBank data from BC, (Frank).
Cap:
2-6(9)cm across, convex to flat, occasionally uplifted and wavy when old; dark vinaceous black, "occasionally dark olivaceous black to brownish black, rarely deep reddish black", "at all times with a paler, whitish beige to yellowish tan band around the margin", "smooth or finely roughened, wrinkled or pitted, finely, densely velvety when young, becoming more matted in age", (Siegel), 2-6(9)cm across, convex to flat, occasionally uplifted and wavy when old; "dark vinaceous black, occasionally dark olivaceous black to brownish black or olive brown to gray, rarely deep reddish black, at all times with a paler, whitish beige to yellowish tan band around the extreme margin"; "smooth or finely roughened, wrinkled or pitted, finely, densely velvety when young", becoming matted to bald when old, (Frank)
Flesh:
thin, firm; "light creamy yellow, not bruising blue", or slightly so in older specimens, (Siegel), in cap "thin, firm, light creamy yellow, not bruising blue, or slightly so in older or waterlogged specimens"; in stem, fibrous, light dingy yellow, reddish at base when old, (Frank)
Pores:
small, "round to slightly angular or irregular"; pale creamy yellow to dingy yellow "or pale yellowish olive when young, becoming dingy yellow to dingy yellow olive, occasionally developing reddish blushes in age", not bruising blue, or occasionally doing so in older, waterlogged specimens; tubes "short to moderately long", sunken around stem to slightly decurrent, (Siegel), 2-4 per mm, "round to slightly angular or irregular", "pale creamy yellow to dingy yellow, or pale yellowish olive when young, becoming dingy yellow to dingy yellow olive, occasionally developing reddish blushes" when old, "not bruising blue, or occasionally erratically so in older, waterlogged specimens"; tube layer sunken around stem to slightly decurrent, (Frank)
Stem:
2-7cm x 0.5-2cm, cylindric or narrowing at the base; yellowish background color, covered extensively with fine rosy red punctations when young, becoming evenly rosy red to dark red when old, (Siegel), 2-7 x 0.5-2cm, cylindric, "or with a tapered base"; yellow background color, covered extensively with fine rosy red punctations when young, becoming evenly rosy red to dark red when old, (Frank)
Taste:
mild to lemony (Siegel, Frank)
Microscopic:
spores 12-15 x 4-5.5 microns, elongate to elliptic, smooth, (Siegel), spores (11.4)12.2-16.7(18.4) x 4.6-6.2(7.2) microns, subfusoid to subcylindric, inequilateral, smooth, inamyloid; basidia 4-spored, 35.3-47.9 x 9.3-12.8 microns, narrowly clavate, colorless; hymenial cystidia rare, 25-50 x 6-11 microns, ventricose to subcylindric, colorless; cap cuticle "a trichoderm with subglobose to ellipsoid underlying cells and clavate to cylindrical awl-shaped terminal cells, often narrower than lower cells", "pigment brown, heavily encrusting in lower cells, parietal in terminal cells"; clamp connections absent, (Frank)
Spore Deposit:
dull olive-brown (Siegel)
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