Pluteus aff. riberaltensis var. missionensis 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 : 91-94

Pluteus aff. riberaltensis var. missionensis Singer , Sydowia 15 (1-6): 123–124, 131 (1962) ( Figs. 46 , 47 )

Diagnosis:—Based on material from Tanna, P. aff. riberaltensis var. missionensis is characterized by an ash brown fibrillose-rimulose pileus with a squamulose disc, and a white basally ash gray flocculose stipe with a subbulbous base. Microcharacteristics include globose basidiospores with a mean size of (5.7 × 4.6 µm), lageniform capitate cheilocystidia, fusoid-ventricose pleurocystidia without or with mucilage, a euhymeniderm-trichoderm pileipellis with brown pigmented lageniform terminal cells overlying a cutis subpellis, narrowly fusiform caulocystidia, and an absence of clamp connections.

Description:— Pileus 28–35 mm diam., convex with a slight umbo with or without a slight central depression, margin slightly sulcate or not; surface dull, dry, densely appressed-fibrillose, disc squamulose-areolate turning radially rimose; squamules, pustules and fibrils ash brown (oac723–oac725) densest and darkest at disc, fading to brown-gray (oac701–oac704) towards the margin with minute streaks of the underlying white context. Context 2–3 mm thick, white. Lamellae free, close, with 2–3 tiers of lamellulae, regular, off-white, turning pale pink (oac760) in maturity. Stipe 42–50 × 3–5 mm, central, cylindrical over a subbulbous base, hollow; surface pearlescent, dry, fibrous, minutely flocculose at the base, surface white to off-white, floccules pale tan (oac760), context white. Odor indistinct. Taste indistinct.

Basidiospores 5–6 × 4–6 µm [x m = 5.66 ± 0.47 × 4.62 ± 0.56 µm, Q = 1–1.5, Q m = 1.24± 0.17, n = 50, s = 1], globose to subglobose, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia 23–32 × 6–8 µm, clavate, 4-spored, hyaline, guttulate, thin-walled, sterigmata 2–4 × 0.5–1 µm. Basidioles 18–23 × 5–8 µm, cylavate to cylindro-clavate, hyaline, guttulate, thin-walled. Lamellar edge sterile. Cheilocystidia 30–64 × 8–13 µm, fusiform to fusoid or clavate, obtuse or capitate, hyaline, thin-walled. Pleurocystidia 35–66 (–80) × 10–20 (–25) µm, fusiform to fusoid-ventricose or narrowly lageniform, some with apical or completely enveloped in mucilage sometimes with adhering spores that obscure view, obtuse or capitate, hyaline, thin-walled. Pileipellis a transition from a euhymeniderm to a trichoderm over a subpellis, composed of a majority of terminal elements 40–69 × 8–12 µm, erect in clusters, especially at the disc, narrowly to broadly lageniform or narrowly fusoid, acute or subcapitate, arising directly from the subpellis or some with one to multiple basal cells, hyaline or with brown plasmatic pigment, non-incrusted, non-gelatinous, thin-walled; subpellis a cutis of repent hyphae, composed of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 3–8 µm diam.. Pileus trama interwoven, composed of hyaline, non-incrusted, non-gelatinous, thin-walled, cylindrical to clavate hyphae, 3–22 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 3–12 µm diam.. Stipitipellis a cutis of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 3–8 µm diam.. Caulocystidia 22–74 × 8–16 µm, often clustered, fusiform to fusoid or lageniform, obtuse or acute, 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 coastal mixed-use agro tree garden and secondary littoral broadleaf forest containing Annona muricata ( Annonaceae ), Artocarpus altilis ( Moraceae ), Barringtonia asiatica ( Lecythidaceae ), Cocos nucifera ( Arecaceae ), Cordia dichotoma ( Boraginaceae ), Euodia hortensis ( Rutaceae ), Leucaena leucocephala ( Fabaceae ), Macaranga dioica ( Euphorbiaceae ), and Musa sp. ( Musaceae ), Vanuatu (Tanna).

Material examined:— VANUATU. Tafea Province: Tanna, Port Resolution. 19°31.459′S, 169°30.340′E, elev. 62 m, 14 August 2019, coll. J. A . del Rosario & B. A . Perry , JAD 281 ( HAY) .

Notes:—The type variety, P. riberaltensis var. riberaltensis Singer (1958: 255) , is only known from the original protologue based on Bolivian material ( Singer, 1958). Based on this original description, the type variety differs from the Vanuatu material by having smaller cheilocystidia (33–44 × 11–16.5 µm), slightly wider pleurocystidia (41–86 × 12.5–39 µm) without mucilage, lacking caulocystidia, and having a cutis pileipellis consisting of cylindrical, rarely attenuate cells. In the same description, Singer proposed P. riberaltensis var. conquistensis Singer (1958: 255) from additional material he acknowledged differed based on the presence of black stripes on the stipe ( Singer 1958). Recently, multiple Pluteus spp . type specimens were re-examined by Rodríguez (2024), including the type P. riberaltensis var. riberaltensis , which differs from this Vanuatu material by having Singer’s observed cutis type pileipellis, lacking the presence of mucilage on any cystidium, and lacking caulocystidia. A specimen of var. conquistensis was reported from Brazil (Menolli et al. 2010) differing based on having moderately longer pleurocystidia closer in size to the type variety. Based on phylogenetic analysis of ITS data ( Fig. 37d ) the Vanuatu material diverges with strong support from the Brazilian specimen of P. riberaltensis var. conquistensis . Comparing the Vanuatu specimen to Singer (1958) and Menolli et al. ’s (2010) material, P. riberaltensis var. conquistensis differs by having shorter and wider cheilocystidia ([27–] 30–47 [–57] × [12.5–] 17.7–27 µm), slightly wider pleurocystidia ([44–] 48–69 [–78] × [15–] 17.5–28 [–35] µm) without mucilage, lacking caulocystidia, a pileipellis arranged as a cutis, and is phylogenetically distinct. The presence of dark fibrils on the stipe was considered exclusive to var. conquistensis , and as this occurs in the Vanuatu specimen, although inconsistently, the reliability of this character is questionable.

Singer proposed another variety, P. riberaltensis var. missionensis Singer (1961: 123) from Argentina ( Singer 1961) that he classified as having a white stipe like the type variety, but differing by the presence of incrustation on cystidia and lacking size differentiation between the pleurocystidia and cheilocystidia. Additional material of P. riberaltensis var. missionensis has also been reported from Mexico ( Cifuentes & Guzmán 1981, Rodríguez 2013). Singer (1961) described the pleurocystidia and cheilocystidia together, regarding their sizes equal (41–69 × 12–22 µm), and by comparison both lamellar cystidia in the Vanuatu material are similarly shaped and roughly equal in length, but the cheilocystidia are slightly narrower. A brief description of Mexican material from the state of Chiapas also describes both the pleurocystidia and cheilocystidia together as equal (67.5–75 × 30–37.5 µm), and these differ from the Vanuatu specimen mainly by being slightly broader and mucilage was not observed ( Cifuentes & Guzmán 1981). Rodríguez re-examined the Chiapas material and provided additional Mexican material from Veracruz and the state of Morelos, but only provided an illustration without a description ( Fig. 10 , Rodríguez 2013). Based on this, compared to the Vanuatu specimen the pileipellis terminal cells appear similarly shaped and arranged, and both lamellar cystidia types appear similarly shaped with both having a type of incrustation/mucilage. Apparently, Rodríguez also re-examined the type variety for comparison, but unfortunately did not provide additional information. Pileipellis terminal elements were not measured or detailed from any of the Mexican material, but Singer’s Argentinean specimen was reported as longer in size (45–160 × 13–26 µm) and described as “appressed…the terminal members often combining to form bunches of ascending hyphae or pyramids which form the fibrils of the pileus” ( Singer 1961). Even navigating Singer’s key from that study requires classifying the pileipellis as a trichoderm to conclude at P. riberaltensis var. missionensis ( Singer 1961) . Based on this, Singer’s pileipellis description is slightly ambiguous and may be loosely interpreted as arranged similar to that in the Vanuatu material. Singer described the type var. riberaltensis as a cutis without specifying the ornamentation of the terminal elements, and var. conquistensis as “…consisting of cylindric hyphae, the terminal members and the cylindric elements anteceding them fuscous and often ascendant,” ( Singer 1958). The Brazilian material of P. riberaltensis var. conquistensis characterized the pileipellis as a cutis “…sometimes with the terminal elements slightly inflated and often ascendant,” (Menolli et al. 2010). Assuming var. conquistensis and var. missionensis were established due to being closely analogous to the type variety, it may be their pileipellis is simply a cutis. The pileipellis arrangement in the Vanuatu material tends to have abundant, erect terminal elements, sometimes with one to multiple basal cells forming a chain, being the predominant feature of the surface and arising from a distinct cutis second layer, and here classified as a euhymeniderm-trichoderm. This contrasts with what this study interprets as a typical cutis arrangement, where the terminal elements may still be repent and integrate themselves into an overall parallel orientation, and sometimes ascending into erect clusters. The Vanuatu specimen is clearly closest to P. riberaltensis var. missionensis based on microscopic similarity with the other descriptions and the mucilaginous cystidia, which may be considered consistent a character for distinction. Singer’s consideration of equal pleurocystidia and cheilocystidia size as a defining feature of var. missionensis may be useful, but the overall defined size range for the variety is unclear as that of Mexican material is slightly larger compared to the Argentinean material, and within the Vanuatu material the cheilocystidia are typically slimmer than the pleurocystidia. The subtly fibrillose stipe, although sparse in some material, would make it closer to var. conquistensis , but this species is phylogenetically distinct and neither account mentions caulocystidia nor cystidia mucilage. Due to Singer’s ambiguous pileipellis classification for P. riberaltensis var. missionensis and vague descriptions from other material, this study prefers to maintain the Vanuatu specimen’s identity as P. aff. riberaltensis var. missionensis . An in-depth re-examination for morphological comparison and molecular sampling for all the varieties, especially the type, are necessary to clarify the relationships and delimitations among the varieties of P. riberaltensis .

Phylogenetic analysis of ITS molecular data ( Fig. 37d ) places the Vanuatu specimen within the general ephebeus clade sensu Menolli et al. (2015b) with a well-supported sister taxon P. flavidus E.F. Malysheva & A.V. Alexandrova (2020: 96) . This recently described Vietnamese species is close to the Vanuatu specimen, particularly in the very similar pileipellis arrangement with fusiform or needle-shaped terminal elements connected to basal cells ( Malysheva et al. 2020). Pluteus flavidus was classified with a hymeniderm with transitions to an epithelium type pileipellis, which may subtly differ from P. aff. riberaltensis var. missionensis as it appears there are more pyriform or epithelioid cells compared to more elongate cells in the Vanuatu specimen. Even so, P. flavidus differs due to more sphaeropedunculate cheilocystidia, lacking mucilaginous pleurocystidia, irregularly shaped caulocystidia, and producing a paler pileus ( Malysheva et al. 2020). The phylogenetically distantly related P. hirtellus Desjardin & B.A. Perry (2018: 612) from São Tomé is superficially similar, but differs by a paler shade of brown, lack of brown fibrils towards the stipe base, smaller more clavate non-capitate cheilocystidia (25–48 × 10–20 µm), more clavate non-mucilaginous pleurocystidia, longer pileipellis elements (48–115 × 8–16 µm), and lack of caulocystidia ( Desjardin & Perry 2018). The Chinese P. squarrosus , shares similar pileipellis terminal elements, but these tend to be longer (50–120 × 7–13 µm) and the species differs in having non-mucilaginous pleurocystidia, shorter cheilocystidia (35–42 × 9–18 µm), and a more grayish brown pileus ( Hosen et al. 2019).

Figures

FIGURE 10. Pluteus vanuatuensis f. ramacystidiatus. 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 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 46. Basidiomes of Pluteus aff. riberaltensis var. missionensis (JAD 281). Scale bar = 10 mm. Photos by: Brian Perry.

FIGURE 47. Pluteus aff. riberaltensis var. missionensis. 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.