Summary:
Cylindrobasidium laeve is recognized macroscopically by 1) the whitish to cream then gray-ochraceous, resupinate fruitbody (or on a vertical substrate, with distinct small caps bent outwards that are whitish and tomentose at first but become green from algae), the spore bearing surface drying characteristically with both radial and circumferential cracks. It is recognized microscopically by 2) tear-shaped spores that tend to agglutinate in groups of 2-4 (smooth, inamyloid, colorless), 3) little-differentiated cystidia, and 4) a monomitic hyphal system, the hyphae with clamp connections and containing numerous oil droplets. The description here is for Cylindrobasidium evolvens, which is a synonym of Cylindrobasidium laeve: "both Burt (1926) and Julich (1974) were convinced that C. evolvens and C. laeve were synonymous", (Chamuris). It is very common in Switzerland (Breitenbach), and common in Scandinavia (Eriksson).

Microscopic:
SPORES 8-12 x 4.3-6 microns, pyriform [pear-shaped], inamyloid, colorless, in some slightly cyanophilic, with a large apiculus, spores often agglutinated; BASIDIA 4-spored, 40-80 x 6-8 microns, cylindric to very narrowly clavate, not distinctly stemmed, always with basal clamp connection, sterigmata about 4-6 x 1-1.5 microns; cystidioles present, sometimes rare, about 60-80 x 6-7.5 microns, fusiform, clamped; HYPHAE monomitic 3-5 microns wide, almost colorless "but the basal and older ones often slightly yellowish-brownish", thin-walled to somewhat thick-walled (up to 0.4-1.0 microns), with clamp connections, guttulate, (Julich), SPORES 8-10(12) x 4-5(7) microns, obliquely ellipsoid to lacrymoid, smooth, inamyloid, colorless, not or only slightly cyanophilic, thin-walled, often agglutinated in groups of 2-4 spores; BASIDIA 4-spored, long and narrowly clavate, mostly 40-50 x 5-6 microns (when young sometimes longer), with basal clamp connection; CYSTIDIA often few and inconspicuous, 50-80 x 5-8 microns, apically borne on basidia-producing hyphae, fusiform, thin-walled, not encrusted; HYPHAE monomitic about 3 microns wide, containing numerous oil-droplets, thin-walled or somewhat thick-walled, colorless or in the basal part yellowish, with clamp connections, SUBICULAR HYPHAE rather straight and parallel to substrate with sparse clamp connections and ramifications [branching], and loosely intertwined, SUBHYMENIAL HYPHAE vertically arranged, densely united, and thinner, (Eriksson), SPORES 8-12 x 5-6(7.5) microns, oval to drop-shaped, smooth, inamyloid, colorless, some agglutinated in small groups, some with granular contents or droplets; BASIDIA 4-spored, 45-65 x 5-7 microns, narrowly clavate, with basal clamp connection; LEPTOCYSTIDIA 45-70 x 5-7 microns, fusiform, smooth; HYPHAE monomitic 3-5 microns wide, thin-walled to thick-walled, some filled with droplets, with clamp connections, (Breitenbach), SPORES 7-12 x 4.5-6 microns, (Ginns(23))

Notes:
Cylindrobasidium laeve has been found in BC, WA, OR, AB, MB, NB, NF, NS, ON, PE, PQ, AK, AZ, CO, DC, GA, MI, MO, NH, NY, and VT, (Ginns(5)). Distribution is also Asia, Europe including Switzerland (Breitenbach) and Scandinavia (Eriksson).

Synonyms and Alternate Names:
Tomentella nigra Hoehn. & Litsch.