Lactifluus auriculiformis Verbeken & F. Hampe
Mycobank number: MB818439
Basidiocarps pleurotoid. Pileus ear- or shell-shaped, at most 7–10 mm diam but often smaller, pure white, smooth, transparently striate. Stipe completely eccentric and very short (1–3 mm), slightly more cream-colored than the pileus. Lamellae white, staining brownish to grayish brown by the latex, in some specimens remarkably few, about 5–7 lamellae per pileus, generally a bit more, with lamellulae. Context white, taste mild. Latex scarce but visible, watery white, staining the lamellae cream to distinctly brownish-grayish after more than 30 min.
Basidiospores subglobose to broadly ellipsoid, (7.4) 7.5–8.3–8.9 × 6.2–6.8–7.3 μm (Q = 1.11–1.22–1.31, n = 30); ornamentation amyloid, composed of rather thick and irregular, rounded ridges, up to 0.6(0.8) μm high, ridges forming a dense and subcomplete reticulum with rather small meshes; plage slightly distally amyloid. Basidia 60–80 × 13–18 μm, cylindrical to narrowly clavate, 4-spored, sterigmata 5–11 × 2–5 μm. Pleuromacrocystidia very abundant, very emergent, 70–120 × 12–14(20) μm, cylindrical and sometimes with rounded apex, or with very small papilla, or fusiform with tapering apex, with slightly refringent walls and distinct acicular, needle-like content. Pleuropseudocystidia abundant, slightly emergent, 3–6 μm diam, slightly tortuous, sometimes branched. Lamella edge substerile, composed of marginal cells and abundant cheilopseudocystidia, with some cheilomacrocystidia and sometimes with small basidia; marginal cells shortly cylindrical to subclavate, 15–28(35) × 7–10 μm; cheilomacrocystidia scarce, clavate, 50–70 × 12–15 μm, with distinct acicular, needle-like content. Hymenophoral trama composed of hyphae mixed with lactiferous hyphae. Pileipellis a lampropalisade to hymeniderm consisting of a layer of rounded cells up to 50 μm thick, with some bearing rounded to subclavate terminal cells, but also with long, hair-shaped, thick-walled elements that sometimes arise deep in the subpellis; hair-like terminal elements 65–190 × 6–12 μm, broader at the base, becoming narrower at the apex, with very thick walls (up to 3 μm thick). Clamp connections absent.
Ecology and distribution: On naked soil on a vertically exposed site underneath Lithocarpus in rainforest dominated by Castanopsis and Lithocarpus polystachyus. Thailand.
Notes: The pileus of Lf. auriculiformis is smooth, but with a good hand lens some hairs (as thick-walled terminal elements in the pileipellis) are visible. The possible sister species Lf. Conchatulus, described from similar habitats in Thailand, differs by smaller spores (6.1–7.8 × 5.1–6.6 μm) and somewhat smaller macrocystidia. However, macrocystidia are mentioned to be only 40–65 μm long in the description of the type, but we did observe macrocystidia up to 80–90 μm long in Lf. conchatulus. Besides the larger macrocystidia, Lf. Auriculiformis has larger and more scattered pileipellis hairs. They measure 65–190 × 6–12 μm compared with 20–70 × 3–6 μm in Lf. conchatulus. The ornamentation of the spores in Lf. conchatulus is a more regular reticulum with wider meshes and regular ridges that have a more equal height. In Lf. auriculiformis, the reticulum is denser with distinctly smaller meshes that are more irregular as the height of the ridges is unequal. The reticulum is incomplete with numerous open ends. Pleuropseudocystidia are abundant and emergent in Lf. auriculiformis but scarce and not emergent in Lf. conchatulus. The margin of the lamellae is substerile in both species, with some scarce basidia present, but mainly composed of marginal cells. In Lf. auriculiformis, cheilopseudocystidia are abundant, cheilomacrocystidia are scarce, whereas in Lf. Conchatulus cheilomacrocystidia are abundant and cheilopseudocystidia hardly observed. The spore ornamentation of Lf. auriculiformis is most similar to the ornamentation in Lf. uyedae, but this species differs by shorter pileipellis hairs (25–70 × 2–6 μm). When we compare Lf. auriculiformis with Lf. genevievae, the latter has spores that are comparable in size (7.1–9.6 × 6.5–8.2) but has a complete and regular reticulum with larger meshes, similar to Lf. conchatulus. Furthermore, macrocystidia in Lf. genevievae are from a completely different type: with a more granular and dense content instead of distinct acicular, needle-like content, and with a fusiform shape very gradually tapering towards the apex.