Lactifluus gerardiellus Wisitrassameewong & Verbeken
Mycobank number: MB818512
Basidiocarps small, fragile. Pileus 3–11 mm diam, applanate to infundibuliform, more or less mucronate in the center, margin striate; edge even; surface dry, velvety, even to slightly wrinkled; sometimes with uneven color ranging from dark brown to reddish brown (7E5, 7F6–7, 8E7–8). Stipe 5–8 mm long, 1–2 mm diam, cylindrical to slightly eccentric, color often paler at apex (5A3, 5B3–B4), white pruinose at base, with hollow pith. Lamellae close, white, with two series of lamellulae. Context <0.5 mm thick in the pileus, cream to pale yellow, not discoloring when bruised, FeSO4 unchanging; taste mild, odor sweetish. Latex rather sparse, white or watery white, unchanging when isolated on glass slide, 10% KOH on latex yellow (4C6); taste mild. Spore print white. Basidiospores subglobose to ellipsoid, mostly broadly ellipsoid, 6.7–7.6–8.4 × 5.4–6.1–6.8(6.9) μm (Q = 1.11–1.25–1.39, n = 30); ornamentation amyloid, composed of ridges and interconnected warts up to 0.5 μm high, forming an incomplete reticulum; plage slightly distally amyloid. Basidia 65–75 × 11–14 μm, cylindrical to subcylindrical, 4-spored. Pleuromacrocystidia absent. Pleuropseudocystidia 3–5 μm diam, slightly tortuous. Lamella edge sterile, composed of marginal cell and abundant cheilomacrocystidia; marginal cells shortly cylindrical to subclavate, often narrow and tortuose, 10–20 × 4–8 μm; cheilomacrocystidia 55–84 × 8–12 μm, fusiform. Hymenophoral trama composed of hyphae,mixed with lactiferous hyphae. Pileipellis a lampropalisade; subpellis consisting of globose to subglobose cells, 15–30 μm diam, forming a dense layer up to 60 μm thick; suprapellis with long, hair-shaped, thickwalled elements, 25–90 × 6–10 μm, broader at the base, becoming narrower at the apex, with dark intracellular pigmentation. Clamp connections absent.
Ecology and distribution: Gregarious among leaf litter in deciduous forest dominated by Castanopsis armata and Quercus. Thailand.
Notes: Lactifluus gerardiellus forms a sister lineage to Lf. indicus. Macroscopically, they differ in habit, as Lf. Gerardiellus is a small agaricoid species whereas Lf. indicus is a pleurotoid species that grows on a subiculum. Microscopically, they differ because Lf. indicus has pileipellis hairs that are shorter (9–48 × 4–7 μm) and more rounded at the apex, shorter basidia (24–51 × 7–13 μm), and a higher spore ornamentation (up to 2.7 μm). Lactifluus gerardiellus is macroscopically similar to Lf. parvigerardii, with paler and more yellowish-brown cap colors. Microscopically, Lf. parvigerardii has spores with a higher ornamentation and a centrally amyloid plage and the terminal elements of the pileipellis are thin-walled and smaller than in Lf. gerardiellus. Lactifluus parvigerardii has pleuromacrocystidia with a more or less rounded apex and no cheilomacrocystidia, whereas Lf. Gerardiellus has only cheilomacrocystidia with a pointed apex. Moreover, in the type collection of Lf. gerardiellus, considerably larger basidia have been observed.