Pluteus petasatus (Fr.) Gillet, 1876

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 : 18-20

Pluteus petasatus (Fr.) Gillet ( Hyménomycètes (Alençon) : 395 (1876) [1878] ( Figs. 4 , 5 )

≡ Agaricus petasatus Fr., Epicr. syst. mycol. (Upsaliae): 142 (1838) [1836–1838]

≡ Pluteus cervinus var. petasatus (Fr.) Fr. , Hymenomycetes europaei: 186 (1874)

Reported heterotypic synonyms:

= Agaricus curtisii Berk. , Hooker’s Journal of Botany and Kew Garden Miscellany 1: 98 (1849)

= Agaricus patricius Schulzer, Icones selectee Hymenomycetum Hungariae per Stephanum Schulzer et Carolum Kalchbrenner observatorum. Magyaroszág Hárta gombák váalogatott Képei 1: 20 (1873)

= Pluteus viscidulus Singer, Lilloa 25: 255 (1952)

= Pluteus straminiphilus Wichanský, Mykol. Sb., Praha : 119 (1968)

= Pluteus australis Murrill, Proceedings of the Florida Academy of Sciences 7 (2–3): 119 (1945)

= Pluteus magnus McClatchie, Proceedings of the Southern California Academy of Sciences 1: 383 (1897)

Diagnosis:—Based on material collected from Tafea Province, P. petasatus is characterized by a dry or viscid, ash brown fibrillose pileus and a white with sparse ash brown fibrils stipe with a subbulbous base. Basidiome variants include some that are white overall, as in JAD 45, or have ash brown floccules at the disc, as in JAD 47. Microscopic characters include broadly ellipsoid spores (7.0 × 4.6 µm), sparse clavate cheilocystidia, fusiform, thick-walled pleurocystidia with 2–4 apical hooks, similar thin-walled intermediate pleurocystidia, an ixo-cutis pileipellis, an absence of caulocystidia, and an absence of clamp connections.

Description:— Pileus 35–80 mm diam., broadly convex, expanding to plano-convex, with or without a broad umbo, with or without a slight central depression; surface dull, dry to moist, the disc glabrous, appressed fibrillose or flocculose, glabrous towards the margin, cream, white to isabelline (oac815–oac816) or pale pink (oac675–oac676), fibrils if present ash brown (oac737–oac739), floccules if present dark ash brown (oac735–oac737). Context 2–4 mm thick, white. Lamellae free, crowded with many tiers of lamellulae, thin (1–2 mm thick), pale pink (oac682–oac683 or oac695–oac697), edges concolorous. Stipe 50–90 mm × 5–15 mm, central, terete, cylindrical above a subbulbous base, solid; surface dull, dry, glabrous to sparsely fibrous, white overall or with ash brown (oac737–oac739) fibrils that tend to become denser towards the base, context white. Odor indistinct. Taste indistinct.

Basidiospores 6–9 (–10) × 4–6 (–8) µm [x mr = 6.18–7.52 × 4.18–4.77 µm, x mm = 6.95 ± 0.69 × 4.56 ± 0.33 µm, Q = 1.16–2.25, Q mr = 1.48–1.59, Q mm = 1.53 ± 0.59, n = 50, s = 3], broadly ellipsoid to subellipsoid, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia 16–26 × 5–10 µm, clavate, 4-spored, hyaline, thin-walled, sterigmata 2–5 × 0.5–1 µm. Basidioles 12–22 × 5–10 µm, clavate to subcylindrical, hyaline, thin-walled. Lamellar edge sterile. Cheilocystidia 18–71 × 8–35 µm, sparse, infrequently forming a well-developed strip on lamellar edge, clavate to narrowly clavate or sphaeropedunculate, obtuse, hyaline, thin-walled. Pleurocystidia; primary pleurocystidia 60–92 × 12–24 µm, fusiform to narrowly utriform, cornuate with 2–4 whole, straight to recurved poorly or well-developed apical hooks, some acute, occasionally with 1–3 lateral hooks, hyaline, evenly thick-walled (up to 2.5 µm thick); intermediate pleurocystidia 38–61 × 8–13 µm, similar to primary pleurocystidia but smaller, fusiform to fusoid, acute or occasionally with 2–3 whole, recurved apical hooks, often with 1–3 lateral excrescences, hyaline, thin to thick-walled (up to 2 µm thick). Pileipellis an ixo-cutis of repent hyphae, embedded in a gelatinous matrix or a cutis with an external gelatinous layer of narrow hyphae, 2–6 µm diam., composed of hyaline or containing brown plasmatic pigment, non-incrusted, gelatinized or not, thin-walled, cylindrical hyphae, 4–18 µm diam.; terminal cells 30–150 × 7–20 µm, repent to erect towards disc, clavate, obtuse, sometimes strongly tapering, seldom with median constriction. Pileus trama interwoven, composed of hyaline, non-gelatinous, thin-walled, cylindrical to inflated hyphae, 9–25 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 4–13 µm diam.. Stipitipellis a cutis, composed of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 5–29 µm diam.. Caulocystidia absent. Clamp connections absent in all tissues examined.

Habitat and known distribution:—Solitary on decaying wood in subtropical coastal scrub, mangrove forest, secondary littoral forest,and lowland mixed-use agro tree garden containing Annona muricata ( Annonaceae ), Artocarpus altillis ( Moraceae ), Barringtonia asiatica ( Lecythidaceae ), Bruguiera gymnorhiza ( Rhizophoraceae ), Cocos nucifera ( Arecaceae ), Cordia dichotoma ( Boraginaceae ), Euodia hortensis ( Rutaceae ), Leucaena leucocephala ( Fabaceae ), Macaranga dioica ( Euphorbiaceae ), Macaranga tanarius ( Euphorbiaceae ), Magnifera indica ( Anacardiaceae ), Musa spp . ( Musaceae ), and Syzygium richii ( Myrtaceae ), Vanuatu (Aneityum, Tanna). Also known from Asia ( Japan, Mongolia, Russia), Europe ( Spain), North America ( Canada, Mexico, United States), South America ( Argentina, Paraguay), and Papua New Guinea.

Material examined:— VANUATU. Tafea Province: Aneityum, along trail from Anelgauhat towards Umej, 20˚14.208′ S , 169˚47.940′E, elev. 26 m, 4 August 2017, coll. M. J . Balick, JAD 45 ( HAY); same location 4 August 2017, coll. J. A . del Rosario & M. C . Aime, JAD 47 ( HAY); Tanna, Port Resolution , trail between Tanna Horizon Bungalow and Ireupow, 19°31.310′S, 169°30.365′E, elev. 7 m, 16 August 2019, coll. J. A . del Rosario & B. A . Perry, JAD 298 ( HAY) .

Notes:— Pluteus petasatus is a species with one of the broadest known distributions within the genus as it has been recorded throughout Eurasia and North America, extending into the Southern Hemisphere. Justo et al. (2014) determined that P. petasatus produces basidiomes with morphologically variable pilei, ranging from dry to viscid, glabrous to variably fibrillose, and having color within a wide spectrum of cream, white, isabelline (pale grayyellow or parchment-colored), and brown to dark gray. Based on molecular evidence and extensive examination of microscopic characters, Justo et al. (2014) proposed multiple species analogous to P. petasatus . The material collected from Aneityum and Tanna fits well within the range of macromorphological characters and consistent microscopic characters under the concept of P. petasatus as defined by Justo et al. (2014).

Phylogenetic analysis based on ITS data ( Fig. 1b ) places the Tafean material with collections from Papua New Guinea and Japan (originally identified as P. magnus McClatchie (1897: 383)) in a well-supported subclade (BS 90 %, PP 0.99) within a larger clade of a global sampling from material identified as P. petasatus . Pluteus magnus had been proposed as a synonym of P. petasatus , despite the absence of molecular data, due to the holotype having identical microcharacters ( Justo et al. 2014). A comprehensive comparison of previous descriptions of P. magnus to the Tafean material reveals identical morphology, except for the Vanuatu specimen’s ixo-cutis pileipellis, which has not been observed in previous accounts ( Banerjee & Sundberg 1993, McClatchie 1897, Singer 1956, Takehashi & Kasuya 2009). Interestingly, the subclade contains collections distributed along the Pacific Ocean from East Asia to Australasia. Collections from Canada ( JN021081 ) and the U.S.A. ( JX857453 ) form a weakly supported subclade (BS 59 %, PP 0.94) sister to the preceding subclade, however this is unsupported. The specimen from the U.S.A. was collected from southern California in the same locality as the type specimen of P. magnus and may possibly serve as topotypical material. Whether or not either of these subclades are representative of P. magnus , and if it should be recognized as a separate species, requires further investigation. Current knowledge indicates that P. petasatus is a widely distributed species occurring in various environments, from disturbed habitats to natural and undisturbed forest, and in drastically different climates, from subtropical to tropical and Mediterranean to temperate. The Vanuatu collections were frequently collected in disturbed coastal forests and according to available records from GenBank, the Papua New Guinea material was collected on the University of Goroka campus. Both the Japanese and Californian collections appear to have been found in urban areas. In these instances, a possible explanation for such a wide distribution may be due to anthropogenic movement of fungal propagules or substrate.

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 4. Basidiome of Pluteus petasatus in situ (JAD 298). Scale bar = 10 mm. Photo by: Brian Perry.

FIGURE 5. Pluteus petasatus. 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.