Russula lilliputia S. L. Mill., Aime & T. W. Henkel 2024, sp. nov.

Russula lilliputia S.L. Mill., Aime & T.W. Henkel sp. nov. (Fig 3) Mycobank: 854388 Diagnosis: Russula lilliputia is characterized by the remarkably small size of its red pileus not exceeding 5 mm, its densely pruinose stipe, and pileus when dry, its restricted distribution in Guyana and basidiome production on the surface of trunks of Dicymbe altsonii trees, spores with relatively indistinct suprahilar plage and occasional scarce, low interconnections between verrucae, long hairlike pileocystidia arising from an epithelioid layer of swollen cells, and white spore print. Etymology: in reference to the diminutive size of the basidiomata – these mushrooms could easily have been part of the mushroom flora of Lilliput encountered in Swift’s Gulliver’s Travels. Holotype: GUYANA. Region 8 Potaro– Siparuni. Pakaraima Mountains, Upper Potaro River Basin, within 15 km radius of Potaro base camp located at 5°18ʹ04.8ʺN 59°54ʹ40.4ʺW, 710–750 m; 23 May 2000, S. L. Miller 10046 (holotype BRG; isotype RMS). GenBank ITS PP741561. Macroscopic description:— Pileus 3–5 mm broad, convex young, then broadly convex, plane or slightly depressed; margin incurved at first, then decurved, entire when young, then frequently lacerate with age, not striate young, sulcate striate when older, striations 1–2 mm in length; pellis dry to moist, pruinose at margin when young, subvelutinous to scurfy in age, disk of primordia pale red to pastel red (9A3–4) with white margin, then brownish red (9C–6–8) overall or with center of disk reddish brown (9E–6–8; 9F6–8), cuticle separability not determined. Lamellae 1–2 mm broad at mid-radius, sinuate, subdistant, not forking at stipe, lamellulae absent but occasionally anastomosing near the cuticle, margin entire, white. Stipe 7.5–10 × 2–3 mm, equal slightly tapered to base, terete to straight cylindrical to slightly curving, attachment central, dry, densely pruinose to subhispid overall, white (i.e., concolorous with lamellae); trama in stipe stuffed, soft. Context in pileus 1 mm at mid-radius soft and pliant, white. Odor not detected. Taste mild, fungal. FeSO 4 yellow on stipe surface. Spore print white. Microscopic description:— Basidiospores 6.8–8 × 6.4–7.2 µm, (x = 7.4 x 6.8 µm, Q = 1.06–1.11, Q m, = 1.0), subglobose to broadly ellipsoid; ornamentation of widely distributed, mostly isolated, acute, narrowly conical elements that are occasionally broader at the base, 1.5(–2) μm high, with scarce low connections, amyloid; suprahilar plage large and verruculose, not decurrent on the apiculus. Basidia (24) 27–29 (–36) × 8–11 (13) μm, clavate to subcylindrical, 4-spored, sterigmata long, 8–12 × 1.6–2 μm. Hymenial cystidia 43–60 × 10–13 μm, subclavate to cylindrical, obtuse to capitate, thin-walled, some long, arising deep within the lamella trama, others shorter, arising in hymenium, emergent 10–35 μm above basidia, scattered to patchy (400–600/mm 2), greyish black in SV. Marginal cells 85–90 × 15–20 μm, fusiform, mucronate, strongly emergent, mixing with small basidia, numerous. Subhymenium well developed of small tightly packed spherical cells of 10 μm diam Lamellar trama composed of many large sphaerocytes, and nests of relatively small, nearly isodiametrical sphaerocytes, interwoven with cylindrical hyphae. Pileipellis orthochromatic in Cresyl Blue, two-layered; subpellis of slightly gelatinized interwoven hyphae of 4–5 μm diam intergrading with discrete regularly spaced rosettes, these often encrusted with reddish brown pigment in KOH; suprapellis arranged in a loose trichoderm from pileus center to pileus margin, composed of frequently branching spindly, digitate hyphae, 5–12 μm diam, cylindrical to clavate, obtuse or capitate and often sinuous and irregularly constricted, often multi-septate, thin- or moderately thickened walls, arising from large inflated, ellipsoidal to spherical cells, 20–35 × 8–20µm, 2–6 deep in aggregate resembling an epithelium, these easily disarticulated in microscopic preparations; Pileocystidia 50–100 μm, long pedicellate, septate, irregularly constricted or swollen at the septum, banded with refringent contents particularly near the septa, moderately thick-walled, arising deep in the trama, SV– or turning pale grey, the contents or interior of the walls acid resistant in BF, no incrustations were observed. Stipitipellis resembling the pileipellis but lacking the swollen elements, composed of dense clusters of long branching, septate, digitate or slightly capitate to irregularly shaped hyphae, and pedicellate, septate, thick-walled caulocystidia that are cylindrical, clavate, obtuse and irregularly constricted. Habit, habitat, and distribution:—Scattered across the trunk surface 1.5 m above the base of a Dicymbe altsonii Sandwith tree. Known only from a single large collection, Upper Potaro Basin of Guyana. We feel confident for several reasons in describing R. lilliputia as a new taxon from a single collection. The type collection was comprised of all stages of basidiome development which included approximately thirty individual basidiomata and primordia distributed across a half-meter-square area of trunk surface 1.5 m above the base of a Dicymbe altsonii tree. The primordia were more numerous than the expanded basidiomata, and the largest basidiomata were never observed to be larger than 5 mm in diameter before beginning to senesce. Importantly, all of the largest basidiomata produced an easily observable white spore print on an acetate sheet, indicating that the basidiomata were mature and not just slightly expanded primordia. BLAST similarity searches on GenBank recovered no close matches. Further, our ITS analyses (not all of which are shown), including all of the red, reddish, or reddish orange Russula collections from our collecting sites in Guyana, along with another newly described red species, R. rubroglutinata S.L. Mill, T.W. Henkel & Aime, ined., included in the present analysis, indicated that R. lilliputia is distinct.