Pluteus cf. fastigiatus Singer

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 : 45-47

Pluteus cf. fastigiatus Singer in Singer & Digilio, Lilloa 25: 259 (1952) ( Figs. 20 , 21 )

Diagnosis:— Pluteus cf. fastigiatus from Tanna is characterized by a campanulate, marginally sulcate dark brown fibrillose-rimose pileus with a dark brown squamulose disc, and a white stipe finely covered with gray fibrils. Microcharacters include subglobose spores (6.2 × 5.0 µm), broadly clavate, acute cheilocystidia, lageniform pleurocystidia, a euhymeniderm pileipellis of broadly clavate cells mixed with fusiform, sometimes thick-walled cells containing brown plasmatic pigment, fusoid-ventricose caulocystidia, and an absence of clamp connections.

Description:— Pileus 45 mm diam., campanulate to convex with a slight umbo, slightly sulcate up to a quarter from margin; surface dull, dry, densely appressed-fibrillose and radially slightly splitting to expose the underlying white context, disc squamulose; squamules and fibrils dark brown (oac638–oac640), darkest and densest at the disc, fading towards margin, underlying surface white to off-white. Context up to 2 mm thick, white. Lamellae free, close with 3–4 tiers of lamellulae, thin, undulate, white to off-white. Stipe 45 × 5 mm, central, terete, cylindrical over a subbulbous base, solid; surface pearlescent, dry, fibrous, fine gray fibrils over a white to off-white surface, context white. Odor indistinct. Taste indistinct.

Basidiospores (5–) 6–7 × (4–) 5–6 µm [x m = 6.2 ± 0.49 × 4.96 ± 0.53 µm, Q = 1–1.5, Q m = 1.26 ± 0.14, n = 50, s = 1], subglobose to broadly ellipsoid, smooth, with a guttule, inamyloid, thick-walled. Basidia 20–30 × 6–10 µm, clavate, 4-spored, hyaline, guttulate, thin-walled, sterigmata 2–4 × 0.5–1 µm. Basidioles 16–25 × 5–10 µm, clavate, hyaline, guttulate, thin-walled. Lamellar edge sterile. Cheilocystidia 40–68 × 13–26 µm, broadly clavate to fusoid-ventricose, obtuse, occasionally acute or subcapitate, hyaline, thin-walled. Pleurocystidia 35–78 × 15–28 µm, scattered, fusiform to lageniform, obtuse, rarely centrally strangulate, hyaline, thin-walled. Pileipellis a euhymeniderm with pileocystidia, composed of a majority of cells 50–90 × 8–28 µm, erect to suberect, clavate to broadly clavate or cylindro-clavate, obtuse or rarely subcapitate, erect to suberect, hyaline or with pale brown plasmatic pigment, non-incrusted, non-gelatinous, thin-walled; pileocystidia 60–112 × 10–18 µm, abundant, erect to suberect, fusiform to lageniform, obtuse or seldom capitate, hyaline or with brown to pale brown plasmatic pigment, thin to sometimes thick-walled. Pileus trama interwoven, composed of hyaline, non-gelatinous, thin-walled hyphae, 8–30 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 4–16 µm diam.. Stipitipellis a cutis, composed of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 5–13 µm diam.. Caulocystidia 40–80 × 8–24 µm, solitary to clustered, fusiform to fusoid-ventricose or clavate, obtuse or occasionally subcapitate to capitate, hyaline, thin-walled. Clamp connections absent in all tissues examined.

Habitat and known distribution:—Solitary on decayed 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, along banks of Numdretum River , 19°38.661′S, 169°25.708′E, elev. 115 m, 30 August 2018, coll. J. A . del Rosario , JAD 170 ( HAY) .

Notes:— Pluteus fastigiatus Singer in Singer & Digilio (1952: 259) is a species currently known only from Argentina ( Singer & Digilio 1952), and although the Vanuatu specimen matches well with many of its characters, the ambiguity of the original description and similarity to other species prevents a conclusive identification. Macromorphologically, the Vanuatu material shares the dark brownish gray fibrillose-rimose pileus with an appressed-squamulose disc. Micromorphologically, the pleurocystidia match in shape, size, and absence of incrustation, the cheilocystidia are similarly shaped and only slightly shorter (21.5–80 × 11.3–30 µm), and the spores are similar in size, but lack “macrospores” (9–11 × 7–8.5 µm) that Singer stated only occurred in carpophores with 1–3-spored basidia ( Singer 1956, 1958, Singer & Digilio 1952). The main differing and ambiguous character is the pileipellis, which based on a compilation of descriptions appears to be a cutis with ascending terminal cells transitioning to a palisade at the disc. This may somewhat resemble the arrangement in the Vanuatu material, which this study prefers to treat as a euhymeniderm as the terminal elements are all erect, or at the least suberect, resembling a palisade throughout the pileipellis. Overall, these terminal elements arise from the interwoven pileus trama with one to two basal septate cells, and are not so much in chains with multiple elongate basal septate cells such as in a typical trichoderm. Pluteus fastigiatus also apparently has no obvious cutis that this study treats as a subpellis or what Singer typically describes as a “hypodermium” ( Singer 1958). From all the descriptions, Singer only provides one illustration of a pileipellis cell ( Fig. 12e , Singer 1956), which is similar to one aspect of the pileipellis elements from the Vanuatu material. Singer emphasized two cell types: broader cells having smaller basal elements and narrow cells being the terminal elements of a longer chain, both being apically rounded. Compared to the Vanuatu material, this may parallel the clavatefusoid and narrowly lageniform elements, respectively. Even the size of these terminal elements in P. fastigiatus are ambiguous, although Singer does not provide measurements in the original circumscription, a misprint from different re-descriptions appears as “53–80 × 16–0 µm” ( Singer 1956) and “43–117 × 8–4.3 µm” ( Singer 1958). Nevertheless, the pileipellis cell length for both overlaps, and it could be assumed that the width of these elements reach at most up to 16 µm, which are both within the Vanuatu material’s size range. A re-examination of the type and additional material to clearly categorize the pileipellis with other characters and sampling for molecular analysis may aid in confirming the identity of this material. For now, it is preferred to tentatively identify the Vanuatu specimen as P. cf. fastigiatus .

Singer considered the predominantly attenuate cheilocystidia, which also occur in the Vanuatu material, in P. fastigiatus to separate it from P. spilopus (Berkeley & Broome) Saccardo (1887: 669) . Pluteus spilopus shares a similar stature to the Vanuatu specimen, but the stipe has distinct black dots that Singer compares to Gomphidius maculatus (Scopoli) Fries (1838: 319) , which may be interpreted as being squamose ( Singer 1956). Pluteus spilopus also differs microscopically due to slightly shorter obtuse cheilocystidia, broadly clavate pleurocystidia, and a repent cutis pileipellis ( Pegler 1986, Singer 1956). The Vanuatu material’s tapered lageniform pileipellis elements may be interpreted as subacute, suggesting comparison to similar taxa with this trait that Singer considered important in establishing his morphological stirps. The Bolivian P. pluvialis Singer (1958: 234) was initially considered for the identity of the Vanuatu material due to similar basidiome stature and similar pileipellis elements. According to the original description, this species also has an ambiguous pileipellis that appears to be a cutis with ascending terminal elements in bunches, but Singer later categorized the species in stirps Fuliginosus which is characterized by a trichodermium type pileipellis with subacute or acuminate terminal cells ( Singer 1958, 1986). Nevertheless, P. pluvialis ultimately differs in the presence of a tomentose pileus, abruptly bulbous stipe, incrusted lamellar cystidia, less lageniform pleurocystidia, and significantly larger pileipellis elements (82–165 × 16.5–19.5 µm) ( Singer 1958). Menolli and Capelari (2016) determined a specimen from Brazil as P. cf. fastigiatus , and this differs from the Vanuatu material by the slightly smaller spores, more clavate incrusted pleurocystidia, lack of caulocystidia, and a cutis pileipellis without obtuse elements.

Figures

FIGURE 12. Pluteus aff. 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.

FIGURE 20. Basidiome of Pluteus cf. fastigiatus (JAD 170). Scale bar = 10 mm. Photo by: Jonathan del Rosario.

FIGURE 21. Pluteus cf. fastigiatus. 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.