Pluteus cf. haywardii Singer, Transactions, 1956

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 : 51-54

Pluteus cf. haywardii Singer, Transactions of the British Mycological Society 39: 147 (1956) ( Figs. 24 , 25 )

Diagnosis:— Pluteus cf. haywardii from Aneityum is characterized by a grayish brown appressed-fibrillose, slightly marginally sulcate pileus, and a similarly colored stipe with a subbulbous base. Microcharacteristics include globose spores (6.7 × 6.1 µm), fusoid cheilocystidia, fusoid pleurocystidia, an ixo-cutis pileipellis with clustered, ascending clavate terminal elements, clavate caulocystidia, and an absence of clamp connections.

Description:— Pileus 10–15 mm diam., convex, margin slightly sulcate; surface dull, somewhat moist, variably appressed-fibrillose typically fading towards the margin or faded at the disc; fibrils pallid tan to grayish brown (oac702–oac704), surface cream-white. Context up to 2 mm thick, white. Lamellae free, moderately close with 2–3 tiers of lamellulae, thin, cream. Stipe 24–30 × 3–4 mm, central, cylindrical over a straight to subbulbous base, hollow; surface dull, dry, fibrous, cream to off-white, with minute streaks concolorous with the pileus surface, context white. Odor not observed. Taste not observed.

Basidiospores 6–7 (–8) × (5–) 6–7 µm [x m = 6.67 ± 0.46 × 6.09 ± 0.44 µm, Q = 1–1.3, Q m = 1.1 ± 0.07, n = 50, s = 1], globose to subglobose, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia 20–30 × 7–9 µm, clavate, 4-spored, hyaline, guttulate, thin-walled, sterigmata 2–4 × 0.5–1 µm. Basidioles 18–25 × 7–9 µm, clavate, hyaline, guttulate, thin-walled. Lamellar edge sterile. Cheilocystidia 32–63 × 7–26 µm, narrowly fusoid to fusoid, or narrowly utriform, obtuse, hyaline, thin-walled. Pleurocystidia 36–63 (–73) × 11–30 µm, narrowly to broadly fusoid-ventricose, or narrowly lageniform to narrowly utriform, obtuse, hyaline, thin-walled. Pileipellis an ixo-cutis of repent hyphae with ascending terminal elements embedded in a gelatinous matrix or gelatinized, composed of hyaline or with pale brown plasmatic pigment, non-incrusted, gelatinized or not, thin-walled, cylindrical hyphae, 12-20 µm diam.; terminal elements (55–) 68–105 × 18–24 µm, typically in fascicles, suberect to erect, clavate to fusoid-ventricose, obtuse, with pale brown plasmatic pigment. Pileus trama interwoven, composed of hyaline, non-gelatinous, thin-walled, cylindrical hyphae, 3–26 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 3–14 µm diam.. Stipitipellis a cutis, composed of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 3–12 µm diam.. Caulocystidia 22–46 × 8–20 µm, in fascicles or sometimes in trichoderm-like chains, clavate or rarely fusoid, obtuse, sometimes with one to three basal cells, hyaline, thin-walled. Clamp connections absent in all tissues examined.

Habitat and known distribution:—Gregarious on wood in subtropical montane primary broadleaf- Araucariaceae / Podocarpaceae rainforest containing Agathis macrophylla ( Araucariaceae ), Balanops pedicellata ( Balanopaceae ), Calophyllum neoebudicum ( Calophyllaceae ), Dendrocnide latifolia ( Urticaceae ), Ficus septica ( Moraceae ), Ficus smithii ( Moraceae ), Garcinia platyphylla ( Clusiaceae ), Geissois denhamii ( Cunoniaceae ), Hernandia moerenhoutiana ( Hernandiaceae ), Macaranga dioica ( Euphorbiaceae ), Podocarpus vanuatuensis ( Podocarpaceae ), Polyscias cissondendron ( Araliaceae ), and Syzygium spp . ( Myrtaceae ), Vanuatu (Aneityum).

Material examined:— VANUATU. Tafea Province: Aneityum, Noposjec , 20°12.420′S, 169°46.795′E, elev. 252 m, 11 December 2019, coll. J. A . del Rosario , JAD 346 ( HAY) .

Notes:— Singer (1956) decided that Patouillard’s species, P. alborubellus (Montagne) Patouillard (1899: 196) , from the Lesser Antilles was erroneously applied to the Montagne species Agaricus alborubellus Montagne (1854: 96) as he found the type to not represent a member of the genus Pluteus . Instead, Singer found Patouillard’s material to match his collection from Argentina, and decided to describe the taxon as P. haywardii Singer (1956: 147) . Additional material has been reported from Martinique and Guadeloupe ( Pegler 1983a) and recollected in Argentina ( Horak 1964, Singer 1961). The Vanuatu material matches closely with the descriptions of P. haywardii , but some morphological discrepancies with the type and very similar morphology to other species prevents a conclusive identification. Singer originally described the pleurocystidia and cheilocystidia together ( Singer 1956, 1958), which are similar in shape but slightly smaller in size (37–55 × 13.7–29 µm equally) compared to the Vanuatu material. Singer also collected additional material close to the type locality, but only observed some of the spores to be more subglobose, with the overall majority still globose compared to the type, and illustrations of the pleurocystidia were provided to include more lageniform-shaped elements ( Singer 1961). The type of P. haywardii also differs from the Vanuatu material by significantly smaller pileipellis elements (37–55 × 13.7–29 µm) and the presence of granules in the form of small fibrils on the pileus surface. Pegler’s material from the Lesser Antilles is more micromorphologically similar to the Vanuatu material, having similarly shaped and sized pileipellis elements and spores, and although the pleurocystidia and cheilocystidia match in shape and size, these are also larger than those of the type ( Pegler 1983a). The additional material reported from Horak (1964) has slightly larger spores and similarly sized pleurocystidia and cheilocystidia, however the pleurocystidia are differently shaped from the cheilocystidia, appearing to be more lageniform with a tapering apex compared to the type, Antillean, and Vanuatu material. Overall, there may be morphological variation within the species, but additional molecular data is necessary to determine this. While Singer describes small fibrils forming granules on the pileus surface, Pegler describes his material as containing squamules at the disc and throughout the pileus, while the surface of the Vanuatu material is glabrous overall, or at least minutely appressed-fibrillose. It must be acknowledged that the basidiomes of the Vanuatu material were not fully expanded when collected, so it is uncertain if expansion may have revealed a similar character or if this trait is important in the taxonomy of P. haywardii .

In the ITS phylogenetic analysis ( Fig. 15a ) the Vanuatu specimen falls in a poorly supported lineage (BS 70 %, PP 0.51) basal to other members of the supported P. semibulbosus (Lasch) Gillet (1876: 395) complex (BS 87 %, PP 1.0). On this branch, JAD 346 falls out with two collections from South Korea identified as P. semibulbosus ( MF437007 , KF668315 ). Pairwise analysis of overlapping ITS regions shows the Vanuatu sequence having 99.64 % similarity to the two South Korean specimens. Superficially, the two share similar basidiome stature, with the South Korean material having a wider pileus (10–25 mm diam.) ( Park et al. 2017). Microscopically, these collections share similarly sized and shaped spores and similarly shaped cheilocystidia, pleurocystidia, and caulocystidia. All three cystidia types are similar in length, but the Vanuatu material generally has broader pleurocystidia and cheilocystidia. Based on micromorphology, JAD 346 is much more similar to the European material identified as P. semibulbosus compared to two other Vanuatu collections identified in this study as P. aff. semibulbosus (see below). Overall, JAD 346 differs in its colored stipe from European collections, and there is little to clearly separate this taxon morphologically from the current concept of P. semibulbosus . The basidiomes of the South Korean material are described with white to cream-colored stipes, but it is unclear if this character is enough to separate them as distinct species from P. semibulbosus .

Due to morphological similarity and overlap among species within Singer’s (1986) stirps, Semibulbosus and the general P. semibulbosus complex, the identity of this Vanuatu species is inconclusive. Clear delimitations need to be established for P. semibulbosus to clearly separate this Vanuatu material. The same can be said for P. haywardii , as contemporary collections, molecular sampling, and re-examination are necessary to refine the concept for this species. Pluteus aquosus Singer (1956: 148) differs based on a white stipe, smaller spores, smaller cheilocystidia, and has subcapitate pleurocystidia ( Singer 1956, 1958). There has been disagreement regarding the concept of Pluteus niveus Murrill (1917: 131) . from the U.S.A. and the type has been re-examined in multiple studies. Smith and Stuntz (1958) and Banerjee and Sundberg (1993) assumed Singer’s (1956) description to be a composite of the type material and a different collection. Based on their concept, P. niveus clearly differs based on a white stipe, more ellipsoid spores, slenderer pleurocystidia, and smaller cheilocystidia ( Banerjee & Sundberg 1993, Smith & Stuntz 1958).

Figures

FIGURE 15a–c. Maximum Likelihood phylogeny of sect. Hispidoderma based on ITS sequence data (-lnL = 7783.640376). 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 24. Basidiomes of Pluteus cf. haywardii (JAD 346). Scale bar = 10 mm. Photo by: Jonathan del Rosario.

FIGURE 25. Pluteus cf. haywardii. 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.