Smithiomyces dominicanus Justo, Angelini & Bizzi 2015, sp. nov.

MycoBank 812588

Diagnosis:—Differs from Smithiomyces mexicanus in the non-umbonate pileus, broad stipe base, smooth basidiospores as seen under light microscope (with isolated small warts under SEM), and nrITS sequence.

Type:— DOMINICAN REPUBLIC. Prov. Puerto Plata: Sosúa, Puerto Chiquito, on humus, 25 November 2011, C. Angelini (CA18 - JBSD 126144 holotype; isotype at MEXU ). nrITS KR604686 (from holotype).

Etymology:— dominicanus refers to the geographic distribution of the species.

Pileus 30–45 mm in diameter, hemispherical or campanulate when young, expanding to convex or plano-convex, without an umbo; surface smooth to innately radially fibrillose, towards the margin with minute, fibrillose-felted to granulose squamules; white, developing yellow or yellow-brown tinges (10YR 8/6, 8/8, 7/6, 7/8) with age or after handling; dry or slightly viscid when moist; margin not striate, appendiculate with abundant, fibrillose remnants of partial veil. Lamellae very crowded, free, segmentiform, up to 1 mm broad; white, developing yellow or yellow-brown tinges with age or after handling; with even or white and flocculose edges. Stipe 30–50× 5–7 mm, cylindrical, with slightly broad or markedly bulbose base; surface white, smooth or with innate longitudinal fibrils; with a membranous, white ring, usually dissociated in patches in the upper third of the stipe. Context in stipe and pileus, white. Smell and taste farinaceous.

Basidiospores [105/5/3] (4)4.5–6 × 2.5–3-(–3.5) μm, avl × avw = 4.9 × 2.7 μm, Q = 1.50–2.40, avQ = 1.81, ellipsoid, oblong or subcylindrical, non-dextrinoid to faintly dextrinoid in Melzer´s, non-metachromatic in Cresyl Blue; the spores appear smooth as observed with a light microscope; under SEM the surface appears smooth, slightly rugose or with isolated, small warts (Fig. 3). Basidia 11–20 × 5–9 μm, tetrasterigmate, clavate. Pleurocystidia absent. Lamellar edge sterile. Cheilocystidia 14–29 × 7–14 μm, clavate to narrowly clavate, hyaline, thin-walled. Pileus covering made up of (sub)globose elements, 21–71 × 20–65 μm, hyaline, with slightly thickened wall; intermixed with cylindrical hyphae, 2–5.5 μm wide. Stipe covering with scattered (sub)globose elements, similar to those on pileus. Clamp connections present and common on the pileus covering, also observed at the base of basidia and cheilocystidia, but not at every septum.

Habit, habitat and phenology:— Gregarious, in groups of 2 to 5 basidiocarps; growing on the humus layer. In broad-leaved forests, with strong anthropogenic influence. November–December.

Distribution:— Only known from two nearby localities in the Dominican Republic.

Additional collections examined:— DOMINICAN REPUBLIC. Prov. Puerto Plata: Sosúa, Playa Sosúa, 19 December 2013, C. Angelini ANGE 180 (JBSD); ibidem, ANGE 181 (JBSD).

Observations:— Smithiomyces dominicanus appears in all phylogenetic analyses (Fig. 1,) as the sister species of S. mexicanus, always with 100% support. The nrITS sequences of both species have a percentage similarity of 87%. In morphological terms both taxa are overall very similar, although S. mexicanus differs from S. dominicanus by having a distinctly umbonate pileus, abundant veil remnants at the stipe base, a non-bulbose stipe base, and rough spores (as seen with a light microscope) that are completely covered in warts (as seen under SEM; see Vellinga 1999). The basidiospores of S. dominicanus appear smooth as observed under light microscope, and under SEM the surface of the spores can either be smooth, rough or with isolated warts that do not completely cover the surface (Fig. 3).

Smithiomyces mexicanus is known from Mexico (Murrill 1911), the state of Florida in the USA (Singer 1944) and Brazil (Horak 1968). It also has been recorded from a Belgian swimming pool, fruiting with imported tropical plants (Vellinga 1999), and from the “Masoala-Hall” in the Zurich Zoo, again with tropical plants (Wilhelm 2015).

There is only one other species in the genus Smithiomyces, S. lanosofarinosus, originally described, and thus far only known, from Brazil (Rick 1939; Raithelhuber 1988). This taxon differs from S. dominicanus by having a white pileus with dark red tints, sulphur yellow lamellae and warty spores as seen under light microscope.

Another tropical, overall white species is Cystolepiota pseudogranulosa (Berk & Broome) Pegler (1986: 583), which differs from S. dominicanus by having a pulverulent pileus surface, smaller basidiocarps (pileus up to 2.5 cm in diameter), cylindrical cheilocystidia, and oblong elements in the pileus covering (Dennis 1952, Pegler 1986; Vellinga 2001a).