Pluteus eugraptoides, 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 : 82-85

Pluteus eugraptoides J.A. del Rosario & B.A. Perry, sp. nov. ( Figs. 40 , 41 )

MycoBank no:—854226

Holotype:— VANUATU. Tafea Province: Tanna, Yanemari , 19°38.294′S, 169°25.568′E, elev. 146 m, 30 August 2018, coll. J. A. del Rosario, JAD 168 ( HAY).

Etymology:—refers to morphological similarities to P. eugraptus .

Diagnosis:— Pluteus eugraptoides from Tanna is characterized by a pale brown hygrophanous pileus with maroon-brown veins radiating from the disc, and a gray stipe with a subbulbous base. Microcharacteristics include subglobose spores (6.7 × 5.5 µm), fusoid-ventricose, cheilocystidia and pleurocystidia, a euhymeniderm pileipellis composed of brown pigmented clavate or sphaeropedunculate, sometimes mucronate cells, clavate or fusoid-ventricose caulocystidia, and an absence of clamp connections. Pluteus eugraptoides closely resembles P. eugraptus (Berkeley & Broome) Saccardo (1887: 678) , but fundamentally differs by lacking marginate lamellae.

Description:— Pileus 15–35 mm diam., hemispherical to plano-convex and papillate; surface dull becoming pulverulent-pellucid-striate, dry, glabrous, disc venose-rugulose, radiating up to one-half of pileus towards margin; veins/wrinkles maroon-brown (oac621–oac623) or concolorous with the surface, surface dull brown (oac722) fading to pale tan (oac675–oac676) towards the margin. Context 3 mm thick, pale tan. Lamellae free, close with 2–3 tiers of lamellulae, slightly thick (up to 2 mm thick), tan (oac675–oac676). Stipe 25–35 × 3–5 mm, central, terete, cylindrical over a subbulbous base, hollow; surface dull, dry, silky, gray to pale tan (oac675–676), context white. Odor indistinct. Taste indistinct.

Basidiospores 5–7 (–8) × 5–6 µm [x m = 6.71 ± 0.79 × 5.51 ± 0.49 µm, Q = 1–1.6, Q m = 1.22 ± 0.15, n = 50, s = 1], subglobose or seldom broadly ellipsoid, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia 22–28 × 5–8 µm, clavate to cylindro-clavate, 4-spored or rarely 2-spored, hyaline, guttulate, thin-walled, sterigmata 1.5–3 × 0.5–1 µm. Basidioles 16–28 × 5–8 µm, clavate to cylindro-clavate, hyaline, guttulate, thin-walled. Lamellar edge sterile. Cheilocystidia 32–46 (–56) × 8–14 (–20) µm, abundant, often clustered, clavate or occasionally lageniform to fusoid-ventricose, obtuse, hyaline, thin-walled. Pleurocystidia (25–) 40–65 (–72) × 12–20 µm, lageniform to fusoid-ventricose, obtuse, hyaline, thin-walled. Pileipellis a euhymeniderm to epithelioid hymeniderm, composed of a majority of cells 25–50 × 10–22 µm, clavate to sphaeropedunculate, obtuse, sometimes mucronate (up to 5 µm long) or rarely nodulose-capitate with 1–2 nodules, with brown plasmatic pigment or sometimes hyaline, non-incrusted, non-gelatinous, thin-walled. Pileus trama interwoven, composed of hyaline, non-incrusted, non-gelatinous, thin-walled, clavate to inflated hyphae, 4–25 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 5–14 µm diam.. Stipitipellis a cutis, composed of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 5–15 µm diam.. Caulocystidia 30–70 × 13–25 µm, clustered to solitary, fusoid-ventricose to clavate, obtuse, hyaline or with brown plasmatic pigment, thin-walled. Clamp connections absent in all tissues examined.

Habitat and known distribution:—Gregarious on rotted 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 (Tanna).

Material examined:— VANUATU. Tafea Province: Tanna, Yanemari , 19°38.294′S, 169°25.568′E, elev. 146 m, 30 August 2018, coll. J. A . del Rosario , JAD 168 ( HAY) .

Notes:— Pluteus eugraptoides has some macroscopic features similar to multiple species, however there are microscopic differences. Pluteus variipes Singer (1956: 218) was collected from Argentina ( Horak 1964, Singer 1956, 1958) and Bolivia ( Singer 1956, 1958) and has a similarly colored pileus, but is overall non-venose, has smaller spores and slightly larger pleurocystidia (34.7–67 × 16–37.5 µm). The Mexican species P. neotropicalis Rodríguez-Alcántar (2008: 274) is also superficially similar, but differs in having slender fusoid cheilocystidia with a long cylindrical projection, narrow subcylindrical pleurocystidia, and narrow fusoid pileipellis elements (Rodríguez et al. 2008). Pluteus chusqueicola Horak (1964: 180) from Argentina is similar in stature, and shares capitate/mammillate pileipellis elements, but these cells tend to have slightly thickened walls and this species also has slightly larger pleurocystidia (60–75 × 16–30 µm) ( Horak 1964).

Pluteus eugraptus is a species originally described from Sri Lanka and later reported from Argentina ( Singer 1956), Bolivia ( Singer 1958), and Tanzania ( Pegler 1977). The type specimen was re-examined ( Justo et al. 2011a) and a collection from Japan (TNSF 12042), was identified as P. cf. eugraptus due to having slightly longer pleurocystidia and cheilocystidia than the holotype, and the lack of additional topotypical material for morphological and molecular comparison.The Japanese material of P. cf. eugraptus differs from the Vanuatu specimen by having longer pleurocystidia and cheilocystidia, pigments in most cheilocystidia and some pleurocystidia, and a lack of caulocystidia. Phylogenetic analysis of ITS data ( Fig. 37a ) places this specimen sister to the Vanuatu material, but with moderate support (BS 74 %, PP 0.98). Compared to the Vanuatu material, P. eugraptus primarily differs by distinct marginate lamellae, slightly shorter pleurocystidia and cheilocystidia, brown pigmented cheilocystidia, lacking a mucronate-nodulose pileipellis, and according to the type re-examination and other studies, an absence of caulocystidia ( Singer 1956, Pegler 1977, Justo et al. 2011a). The lack of pigments on the lamellar edge, pileipellis with apical ornamentation, and presence of caulocystidia clearly separate the Vanuatu material from P. eugraptus and the Japanese P. cf. eugraptus , as well as being molecularly distinct from the latter. In addition, a closely related species in P. pseudeugraptus Horak (1967: 187) of Argentina is microscopically close with similarly shaped cheilocystidia and pleurocystidia, however this species was not reported with caulocystidia, has slightly wider pleurocystidia, pigmented cheilocystidia, a unicolored darker brown pileus, and marginate lamellae ( Horak 1964).

Pluteus eugraptoides appears to share a relationship with P. phlebophorus (Ditmar) Kummer (1871: 98) and its allies, which is a taxonomically difficult group due to a high degree of morphological variability and the absence of type specimens. Phylogenetic analysis ( Fig. 38a ) places the Vanuatu specimen within the chrysophlebius / phlebophorus clade sensu Justo et al. (2011b). Based on current knowledge of P. phlebophorus the species appears to have a widespread temperate distribution throughout Eurasia and the northeastern United States and is otherwise morphologically distinct in having larger pleurocystidia and cheilocystidia, and lacking a mucronate-capitate pileipellis ( Breitenbach & Kränzlin 1995, Homola 1972, Minnis & Sundberg 2010, Orton 1986). Pluteus hendersoniensis Singer (1989: 793) is one of the few Pluteus spp . reported from the South Pacific, being from Henderson Island ( Pitcairn Islands), and exhibits close features comparable to members of the chrysophlebius / phlebophorus clade and the Vanuatu specimen ( Singer 1989). Compared to P. eugraptoides , the pileus color and ornamentation of P. hendersoniensis is similar, but differs based on the white stipe and smaller stature (pileus 7.5–15 mm, stipe 11 × 0.5 mm). Additionally, the terminal elements of the pileipellis are non-mucronate and significantly smaller (20–30 × 11.5–25 µm), and both cheilocystidia and pleurocystidia are much smaller compared to the Vanuatu material, which Singer described as undifferentiated in size and the same as that of the pileipellis ( Singer 1989).

Figures

FIGURE 37a–e. Maximum Likelihood phylogeny of sect. Celluloderma based on ITS sequence data (-lnL = 18618.671374). 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. Only values greater than 70/0.70 are shown. Nodes receiving support values greater than 90/0.95 are highlighted in bold.

FIGURE 38. Basidiomes of Pluteus aff. argentinensis (JAD 301). Scale bar = 10 mm. Photos by: Brian Perry.

FIGURE 40. Basidiomes of Pluteus eugraptoides (JAD 168 holotype). Scale bar = 10 mm. Photos by: Jonathan del Rosario.

FIGURE 41. Pluteus eugraptoides. a. Basidiospores. b. Basidia. c. Basidioles. d. Pileipellis terminal elements. e. Cheilocystidia. f. Caulocystidia. g. Pleurocystidia. Scale bar = 10 µm. Drawings by: Jonathan del Rosario.