Pluteus vanuatuensis, Del, Jonathan A. & Perry, Brian A., 2025

Del, Jonathan A. & Perry, Brian A., 2025, The genus Pluteus (Basidiomycota, Agaricales, Pluteaceae) from Tafea Province, Republic of Vanuatu, Phytotaxa 709 (1), pp. 1-104 : 23-26

Pluteus vanuatuensis J.A. del Rosario & B.A. Perry, sp. nov. ( Figs. 7 , 8 )

MycoBank no.:—854222

Holotype:— VANUATU. Tafea Province: Tanna, Numdretum River , 19°38.246′S, 169°25.237′E, elev. 145 m, 4 December 2018, coll. J. A. del Rosario, JAD 189 ( HAY).

Etymology:—Refers to the Vanuatu islands where the holotype was collected.

Diagnosis:— Pluteus vanuatuensis from Tafea is distinguished by a grayish brown to hazel appressed-fibrillose, black floccose-pustulate disc, hygrophanous and sulcate pileus, and a white stipe with pale brown minute streaks and a bulbous base. All tissues bruise a faint bluish gray. Microcharacters include subglobose basidiospores (7.3 × 6.6 µm), clavate cheilocystidia, fusoid, thick-walled pleurocystidia with 2–5 apical hooks, similar but smaller intermediate pleurocystidia, a cutis pileipellis with erect clavate terminal elements at the disc, absent caulocystidia, and the presence of clamp connections in all tissue.

Description:— Pileus 25–70 mm diam., hemispherical to plano-convex with a slight centrally depressed umbo; surface dull to pellucid-striate up to half-way from margin, hygrophanous, finely appressed-fibrillose to subglabrous, disc floccose-pustulate; floccules/pustules/fibrils dark chocolate brown (oac639–oac641) to brown-black, underlying surface dull gray-brown (oac730–oac736/oac720–oac722) turning pallid brown (oac751–oac753) to pale hazel (oac646–648) towards margin. Context up to 1.5 mm thick, pallid gray-brown turning faintly bluish gray when exposed. Lamellae free, moderately close with 3 tiers of lamellulae, thin (up to 1 mm thick), light pink (oac632–oac634/oac696– oac697). Stipe 40–60 × 3–4 mm, central, terete, cylindrical above a subbulbous to bulbous base, hollow; surface pearlescent, dry, silky, white to off-white without or infrequently with tannish brown (oac672–oac675) tones mid-way towards the base, occasionally with bluish gray tones at the base, context white. Tissues turning bluish gray when disrupted or handled. Odor indistinct. Taste indistinct.

Basidiospores (5–) 6–8 (–9) × (5–) 6–7 (–8) µm [x mr = 6.98–7.56 × 5.98–6.94 µm, x mm = 7.26 ± 0.23 × 6.49 ± 0.35 µm, Q = 1–1.5, Q mr = 1.04–1.18, Q mm = 1.12 ± 0.04, n = 50, s = 6], globose to subglobose, rarely broadly ellipsoid, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia (15–) 18–34 × 6–8 µm, clavate, 4-spored or rarely 2-spored, hyaline, thin-walled, sterigmata 2–3 × 0.5–1 µm. Basidioles 16–35 × 6–10 µm, clavate, hyaline, thin-walled. Lamellar edge sterile. Cheilocystidia 30–75 × (8–) 15–24 µm, clavate or seldom sphaeropedunculate or utriform, obtuse or seldom subcapitate, hyaline, thin-walled. Pleurocystidia; primary pleurocystidia 50–102 × 12–25 µm, fusoid to narrowly lageniform, apex variable, cornuate or corniculate with 2–4 (–5) whole to bifid, straight or recurved poorly or well-developed apical hooks, bifid frequency varying among specimens with acute, cornuate or corniculate arms, most with a guttule, rarely asymmetrical, hyaline, thin to thick-walled (up to 2 µm thick); intermediate pleurocystidia 33–66 × 11–25 µm, fusoid to lageniform or seldom utriform, obtuse, acute or corniculate to rarely cornuate with 1–4 whole, blunt, straight to recurved poorly developed apical hooks, with a guttule, hyaline, thin to thick-walled. Pileipellis a cutis of repent hyphae, composed of grayish brown plasmatic pigment or hyaline, non-incrusted, non-gelatinous, thin-walled, cylindrical hyphae, 5–20 µm diam.; terminal elements 45–135 (–180) × 11–18 µm, in erect fascicles at the disc, clavate or filiform, obtuse, rarely strongly tapering or subcapitate, rarely entirely nodulose (one collection), hyaline or with grayish brown plasmatic pigment, thin-walled. Pileus trama interwoven, composed of hyaline, non-gelatinous, thin-walled, cylindrical to inflated hyphae, 7–25 (–35) µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 5–22 µm diam.. Stipitipellis a cutis, composed of hyaline or sometimes with grayish brown plasmatic pigment, non-incrusted, non-gelatinous, thin-walled hyphae, 3–18 µm diam.. Caulocystidia absent. Clamp connections present in all tissues examined.

Habitat and known distribution:—Gregarious to solitary on decaying wood in subtropical lowland mixed-use agro tree garden and secondary broadleaf rainforest containing Bischofia javanica ( Phyllanthaceae ), Burckella obovata ( Sapotaceae ), Claoxylon gillisonii ( Euphorbiaceae ), Dendrocnide latifolia ( Urticaceae ), Didymocheton spp . ( Meliaceae ), Ficus spp . ( Moraceae ), Garcinia pseudoguttifera ( Clusiaceae ), Homolanthus nutans ( Euphorbiaceae ), Macaranga dioica ( Euphorbiaceae ), and Syzygium nomoa ( Myrtaceae ), Vanuatu (Aneityum, Tanna).

Material examined:— VANUATU. Tafea Province: Tanna, Numdretum River , 19°38.440′S, 169°25.385′E, elev. 131 m, 29 August 2018, coll. J. A . del Rosario , JAD 160 ( HAY); Tanna, Yanemarei, 19°38.511′S, 169°25.616′E, elev. 94 m, 30 August 2018, coll. J. A . del Rosario, JAD 169 ( HAY); Tanna, Numdretum River , 19°38.246′S, 169°25.237′E, elev. 145 m, 4 December 2018, coll. J. A . del Rosario , JAD 189 ( HAY); Tanna, Tangahuruti, 19°38.809′S, 169°26.382′E, elev. 66 m, 6 December 2018, coll. J. A . del Rosario , JAD 215 ( HAY); Aneityum, Nathaway, 20°14.245′S, 169°48.177′E, elev. 0 m, 10 December 2018, coll. J. A . del Rosario , JAD 229 ( HAY); Tanna, Yakuwan, 19°32.230′S, 169°28.911′E, elev. 84 m, 15 August 2019, coll. J. A . del Rosario & B. A . Perry , JAD 286 ( HAY) .

Notes:—The distinctive bluish gray bruising of disrupted tissue from this species requires comparison to similar species, such as P. salicinus (Persoon) Kummer (1871: 99) , P. saupei Justo & Minnis (2011: 475) , and P. americanus (Banerjee & Sunderberg) Justo, E.F. Malysheva & Minnis (2014: 180) . The Eurasian P. salicinus differs in having a grayer pileus, smaller ellipsoid spores, less versiform pleurocystidia with developed apical hooks, intermediate pleurocystidia lacking apical hooks, and more clavate cheilocystidia ( Justo et al. 2014). Known only from the state of Illinois in the U.S.A., P. saupei shares the outward appearance of P. vanuatuensis , but microscopically differs by having slightly larger ellipsoid spores, pleurocystidia with poorly developed hooks, and more lageniform cheilocystidia with elongated apices ( Justo et al. 2011b). Pluteus americanus was originally described as a variety of P. salicinus before being elevated to species rank based on molecular data and geographic distinction by being known from the eastern United States and Russian Far East ( Banerjee & Sundberg 1993, Justo et al. 2014). Pluteus americanus is also superficially very similar to the Vanuatu specimen, but differs with its lighter-colored pileus, more ellipsoid spores, less apically versiform pleurocystidia, non-apically hooked intermediate pleurocystidia, and the absence of utriform or umbonate cheilocystidia ( Justo et al. 2014). Some additional tropical species share similarities to P. vanuatuensis , but fundamentally differ in lacking blue-gray bruising. From Papua New Guinea, P. kobayasii Hongo (1976: 100) is one of the few species of Pluteus known from Vanuatu’s neighbouring region. Although this taxon has a similarly colored pileus and contains clamp connections in the hyphal tissue, it differs by lacking a floccose disc or a pellucid-striate margin, is slightly smaller in stature, has fusoid thick-walled cheilocystidia, and lacks apically variable pleurocystidia ( Hongo 1976).

The type of P. saupei was originally identified as a specimen of P. salicinus , and the material from both species was used to demonstrate the presence of the psychotropic compound psilocybin for the first time in a species of Pluteus ( Saupe 1981) . Psilocybin expression and similar blue bruising reactions arose independently in multiple lineages throughout the evolutionary history of fungi ( Guzmán et al. 1998). These same blue, gray, or sometimes green-toned bruising reactions have been shown to originate at least twice in the evolution of the genus Pluteus , as this character is known to occur in P. cyanopus Quélet (1883: 391) and P. phaeocyanopus Minnis & Sunderberg (2010: 44) of sect. Celluloderma , and members of the P. glaucotinctus Horak (1976: 88) complex, which falls in the salicinus / albostipitatus clade recognized by Justo et al. (2011b) ( Justo et al. 2014, Minnis & Sundberg 2010). Currently, the presence of psilocybin has only been confirmed in certain species within the salicinus / albostipitatus clade, and not all members, such as the aforementioned P. albostipitatus , have been observed to exhibit a similar bruising reaction ( Menolli et al. 2014).

Based on ITS molecular data ( Fig. 1c ), P.vanuatuensis is phylogenetically placed within the salicinus / albostipitatus clade recognized by Justo et al. (2011b). This relationship to other members of this group known to display a blue bruising reaction and produce psilocybin or allied compounds raises the question if the compound is produced by P. vanuatuensis as well. Among all the specimens made during this study, P. vanuatuensis is represented by the highest number of collections, and observations conclude that it is a morphologically variable species. Pleurocystidia display a wide variety of apical ornamentation without a distinct dominant type, ranging from well to poorly developed cornuate, corniculate, bifid, or obtuse. Phylogenetic analysis ( Fig. 1c ) places these collections in a well-supported clade with two distinct lineages: one is strongly supported ( BS 100 %, PP 1.0) containing collections JAD 169, JAD 189, and JAD 229, another is moderately supported ( BS 83 %, PP 0.99) containing collections JAD 160, JAD 215, JAD 159, and a Vietnamese specimen of P. sp. 1 ( OQ 732732). Comparison of the Vanuatu specimens with the description of the Vietnamese specimen ( Malysheva et al. 2023) indicates that the collections of these two clades show no discernible morphological differences to clearly separate them, except collection JAD 159 which has enough different morphological features to warrant treatment as a separate taxonomic unit discussed in the following section. A pairwise analysis of the overlapping region of JAD 159 against both lineages showed a 90.37–90.75 % similarity when indels were included and a 93.06–94.03 % difference when indels are excluded. Unfortunately we were not able to produce ITS data for JAD 286 due to a high number of indels, but tef1 data was successfully generated. The identity of JAD 286 as P. vanuatuensis is confirmed based on analysis of tef1 data ( Fig. 6c ) and morphological similarity. One collection, JAD 285, is positioned outside of this clade in both analyses for the wider sampled ITS dataset, but this is weakly supported ( ML 59 %, PP 0.66). The phylogenetic affinity of JAD 285 results in preference to treat it as a separate taxonomic unit, which will be discussed in the proceeding section as P. aff. vanuatuensis .

Figures

FIGURE 1a–d. Maximum Likelihood phylogeny of sect. Pluteus based on ITS sequence data (-lnL = 6609.645735). Sequences of specimens from Vanuatu are indicated in bold type. Stars indicate type specimens. Values separated by / refer to ML bootstrap proportions and Bayesian posterior probabilities, respectively. Only values greater than 70/0.70 are shown. Nodes receiving support values greater than 90/0.95 are highlighted in bold.

FIGURE 6a–c. Maximum Likelihood phylogenies of the albostipitatus/salicinus clade based on combined (Fig. 6a; -lnL = 4927.663337), ITS (Fig. 6b; -lnL 2206.25101), and tef1 (Fig. 6c; -lnL = 2099.291416) sequence data. Sequences of specimens from Vanuatu are indicated in bold type. Stars indicate type specimens. Values separated by / refer to ML bootstrap proportions and Bayesian posterior probabilities, respectively. Only values greater than 70/0.70 are shown. Nodes receiving support values greater than 90/0.95 are highlighted in bold.

FIGURE 7. Basidiomes of Pluteus vanuatuensis (JAD 189 holotype). Scale bar = 10 mm. Photo by: Jonathan del Rosario.

FIGURE 8. Pluteus vanuatuensis. a. Basidiospores. b. Basidia. c. Basidioles. d. Pileipellis terminal elements. e. Cheilocystidia. f. Intermediate pleurocystidia. g. Primary pleurocystidia. Scale bar = 10 µm. Drawings by: Jonathan del Rosario.