Pluteus albostipitatus (Dennis) Singer, Lloydia, 1958

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 : 14-18

Pluteus albostipitatus (Dennis) Singer, Lloydia 21: 240 (1959) ( Figs. 2 , 3 )

≡ Pluteus spilopus var. albostipitatus Dennis , Bulletin de la Société Mycologique de France 69(2): 195 (1953)

Reported heterotypic synonyms:

= Pluteus phaeoleucus E. Horak , Bulletin du Jardin Botanique National de Belgique 47(1–2): 89 (1977)

= Pluteus melanopotamicus Singer, Fieldiana, Bot. 21: 96 (1989)

= Pluteus densifibrillosus Menolli & Capelari, Mycologia 102(2): 698 (2010)

Diagnosis:—Based on material from Aneityum, P. albostipitatus is characterized macroscopically by a gray-brown, variably fibrillose, centrally punctate pileus and a white stipe. Microscopically it is characterized by subglobose to broadly ellipsoid spores (8.1 × 6.2 µm), clavate cheilocystidia, fusoid, thin to thick-walled pleurocystidia with 2–6 apical hooks, a cutis pileipellis, and the absence of caulocystidia.

Description:— Pileus 35–37.5 mm diam., plano-convex to broadly plano-convex, margin entire or splitting; surface somewhat pearlescent, dry, disc pustulate or warted with agglutinated hairs, variably appressed-fibrillose; disc gray-brown (56E3–4), fibrils gray (5DE2–3) towards margin, underlying surface pallid gray. Context thin, pallid gray. Lamellae free, close with 2 tiers of lamellulae, moderately broad (3–4 mm), white-gray to pink-gray with brown tones (6–7B2–3), margin paler, slightly eroded. Stipe 32–47 × 2.5–3 mm, central, terete, cylindrical above a subbulbous base (4–6 mm), solid; surface pearlescent, dry, silky, pallid white-gray with brown tones towards base and where handled, context white. Odor indistinct. Taste not observed.

Basidiospores (5–) 6–11 (–13) × 5–8 (–9) µm [x mr = 7.41–8.88 × 6.12–6.3 µm, x mm = 8.15 ± 1.0 × 6.21 ± 0.62 µm, Q = 1–1.6 (–2.0), Q mr = 1.21–1.42, Q mm = 1.31 ± 0.25, n = 50, s = 2], subglobose to broadly ellipsoid, seldom globose, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia 15–35 × 6–11 µm, subclavate to cylindro-clavate, 4- spored, hyaline, thin-walled, sterigmata 2–5 × 0.5–1 µm. Basidioles 11–25 × 4–10 µm, clavate to subclavate, hyaline, thin-walled. Lamellar edge sterile. Cheilocystidia 24–60 × 8–22 µm, clavate to subclavate or fusoid-ventricose to sphaeropedunculate, obtuse or subcapitate to umbonate, hyaline, thin-walled. Pleurocystidia 53–110 × 6–22 µm, common, fusiform to fusoid-ventricose or seldom utriform to broadly clavate, obtuse to truncate without outgrowths, with 2–4 clefts, or infrequently corniculate with 2–6 whole or bifid, blunt, recurved poorly-developed apical hooks, rarely asymmetrical, hyaline, some with a guttule, thin to thick-walled (up to 2 µm thick) often thinning towards the base. Pileipellis a cutis of repent hyphae, composed of hyaline or pale to dark brown plasmatic pigment, non-incrusted, non-gelatinous, thin-walled, cylindrical hyphae, 4–20 (–25) µm diam.; terminal elements 35–111 × 7–22 µm, suberect to erect towards disc and repent elsewhere, cylindrical to clavate, obtuse or infrequently subcapitate. Pileus trama interwoven, composed of hyaline, non-gelatinous, thin-walled, cylindrical to inflated hyphae, 3–28 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 3–20 µm diam.. Stipitipellis a cutis, composed of hyaline, non-incrusted, non-gelatinous, thin-walled hyphae, 3–20 (–25) μm diam.. Caulocystidia absent. Clamp connections present sometimes in stipitipellis tissue, and absent in all other tissues.

Habitat and known distribution:—Solitary on decaying wood in subtropical coastal scrub,mangrove forest,secondary littoral forest,and mixed-use agro tree garden containing Annona muricata ( Annonaceae ), Artocarpus altillis ( Moraceae ), Bruguiera gymnorhiza ( Rhizophoraceae ), Cocos nucifera ( Arecaceae ), Macaranga tanarius ( Euphorbiaceae ), Magnifera indica ( Anacardiaceae ), Musa spp . ( Musaceae ), and Syzygium richii ( Myrtaceae ) or 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). Also known from Africa (D.R. Congo, São Tomé), Asia ( Thailand, Vietnam), Caribbean (Martinique, Trinidad), South America ( Argentina, Bolivia, Brazil, French Guiana, Galapagos Islands), and North America ( United States, Florida, Indiana).

Material examined:— VANUATU. Tafea Province: Aneityum, Anloulanelcau area , trail through mixed forest to transect 11, 20°13.066′S, 169°47.406′E, elev. 188 m, 29 July 2017, coll. B. A . Perry, BAP 930 ( HAY); Aneityum, along trail from Anelgauhat towards Umej , 20°14.202′S, 169°48.203′E, elev. 26 m, 7 August 2017, coll. M. C . Aime , BAP 968 ( HAY) .

Notes:—A survey of multiple descriptions of P.albostipitatus (Dennis) Singer (1958:240) reveals a morphologically cryptic species with wide macroscopic and microscopic variation, as also acknowledged by previous authors ( Desjardin & Perry 2018, Menolli & Capelari 2010, Menolli et al. 2015a). Originally described from Trinidad as P. spilopus var. albostipitatus Dennis (1953: 195) before being elevated to species rank by Singer (1958), the species was initially placed in sect. Hispidoderma due to early collections generally displaying thin-walled pleurocystidia with truncate, hookless apices ( Dennis 1953). Singer reported small apical outgrowths on pleurocystidia from Argentinean material, and both he and Pegler suspected that this atypical shape had an intermediate link to metuloid cystidia found in species of sect. Pluteus ( Pegler 1983 a, Singer 1958). Phylogenetic studies have confirmed the position of P. albostipitatus within sect. Pluteus as part of the salicinus / albostipitatus clade recognized by Justo et al. (2011b), which includes other species containing thin-walled pleurocystidia with poorly developed apical hooks that are considered atypical for the section ( Justo et al. 2011b, Menolli & Capelari 2010). Recent descriptions of this species by Menolli et al. (2015a) and Desjardin and Perry (2018) display the extent of microcharacter variation within the species, and provide additional instances of pleurocystidia with poorly developed apical outgrowths and thin to thick walls similar to those seen in the Vanuatu specimens.

Based on multiple descriptions, the current concept of P. albostipitatus defines the pileus as morphologically variable, with the surface ranging from densely appressed-fibrillose to completely smooth and glabrous ( Justo et al. 2011b, Menolli et al. 2015a, Singer 1956). Desjardin and Perry (2018) reported the pileus disc being appressed-fibrillose, but glabrous to subglabrous elsewhere, and Singer noted collections appearing subglabrous when wet, but typically “when fresh and dry more or less distinctly radially fibrillose with innate fibrils” ( Singer 1956). Referring to a photo of Desjardin and Perry’s São Tomé material ( Fig. 7 , 2018), the material appears older and wet, possibly similar to Singer’s observations, and is an example of the influence of environmental factors on superficial appearance during collecting. The material from Aneityum appears as appressed-fibrillose with shades of gray to grayish brown, matching descriptions from multiple authors ( Dennis 1953, Horak 1964, Menolli & Capelari 2010, Menolli et al. 2015a, Singer 1956). Species such as P. phaeoleucus Horak (1976: 89) from the D.R. Congo ( Horak 1976) and P. densifibrillosus Menolli & Capelari (2010: 698) from Brazil ( Menolli & Capelari 2010), that are recognized as synonymous with P. albostipitatus ( Menolli et al. 2015a) were described with a non-striate pileus, similar to the Vanuatu material. In contrast, other authors have described the pileus as being striate to sulcate ( Dennis 1953, Desjardin & Perry 2018, Horak & Heinemann 1978, Menolli et al. 2010, Pegler 1983a, Singer 1956). All prior mentioned accounts also describe the pileus center as punctate, nippled or some variation, and this occurs in the Aneityum material.

In P. albostipitatus , spore shape has been observed to range from globose to broadly ellipsoid, and the predominant shape and size may be dependent on the specimen. Overall, the Vanuatu material displays spore sizes within previously reported ranges, although collection BAP 968 was observed to consist of more broadly ellipsoid spores versus BAP 930 having predominantly subglobose spores. Size and morphological variation of microcharacters extends to the pleurocystidia and cheilocystidia in both Vanuatu specimens. Both collections contain thin to thick-walled (up to 2 µm thick) pleurocystidia that are predominantly fusiform to fusoid-ventricose in shape, matching previous accounts ( Desjardin & Perry 2018, Horak 1964, Menolli & Capelari, 2010, Menolli et al. 2015a, Pegler 1983 a, Singer 1958). Both Aneityum collections also contain apically obtuse pleurocystidia, but the predominant apex type on pleurocystidia differs between specimens. BAP 930 has more pleurocystidia with poorly developed outgrowths on the apices, like those described by Singer (1958), Menolli et al. (2015a), and Desjardin and Perry (2018). BAP 968 has more pleurocystidia with truncate apices, like those in Pegler (1983a), also in Desjardin and Perry (2018), and bifid apices as in Menolli & Capelari (2010), Menolli et al. (2015a), and Desjardin and Perry (2018). Both Aneityum collections also contain rarely observed broadly clavate to broadly utriform pleurocysitida, which appear to be the predominant type in descriptions by Horak ( Horak & Heinemann 1978) and Menolli et al. (2015a). Cheilocystidia observed in the Vanuatu collections also match the size and shape from prior accounts, however in collection BAP 930 a subcapitate-umbonate apex type occurs that has not been previously reported. The clearly extensive morphological variation in the current concept of P. albostipitatus requires further inquiry and suggests that cryptic species could be hiding under this name.

Phylogenetic analysis of ITS data places one of the Vanuatu specimens, BAP 968, within a low supported clade ( Fig. 1c , BS 69 %, PP 0.86) with poorly resolved internal topology comprised of sequences identified as P. septocystidiatus Ševčíková, Antonín & Borovička (2014: 230) from South Korea, Thailand, Vietnam, and the United States (New York, Indiana, and Florida), P. cf. septocystidiatus from Florida, U.S.A., P. aff. septocystidiatus from Vietnam, and P. albostipitatus from São Tomé. BAP 930 was not included in the analysis due to multiple failed attempts at sequencing ITS because of a high number of indels. Pluteus septocystidiatus is a recently described species from Korea and the U.S.A. (Florida) that is distinguished primarily by fusiform, relatively thick-walled pleurocystidia with distinctive medial septa ( Ševčíková et al. 2014). Ševčíková et al. included two collections from Florida that were originally identified as P. albostipitatus . AJ154 ( HM562057 ) contained distinctly thick-walled septate pleurocystidia as well as thin-walled pleurocystidia with obtuse projections similar to those known in P. albostipitatus . AJ187 ( HM562106 ) was tentatively identified as P. cf. septocystidiatus due to having a minority of septate pleurocystidia never being distinctly thick-walled and being phylogenetically distant from the other collections of P. septocystidiatus . Singer noted in his description of P. albostipitatus that the pleurocystidia are characterized “exceptionally with a pseudo-[secondary] septum near the tip” ( Singer 1958), which Ševčíková et al. considered when proposing P. septocystidiatus distinct from P. albostipitatus . In addition to septate pleurocystidia, the rare presence of clamp connections on the stipitipellis was also used as a distinct feature, and this character occurs in the Vanuatu material. The specimen of P. septocystidiatus from Thailand was described as having septate pleurocystidia, but lacking clamp connections in all tissues including the stipitipellis ( Wannathes et al. 2022). The material from New York, U.S.A., provided a single photo with a septate pleurocystidia (iNaturalist 55850102). The Vietnamese material identified as P. septocystidiatus was described as predominantly having septate pleurocystidia while the specimen distinguished as P. aff. septocystidiatus was described as also having septate pleurocystidia, but to a lesser extent ( Malysheva et al. 2023). Desjardin and Perry (2018) observed their São Tomé specimen of P. albostipitatus having non-septate, apically obtuse, thin-walled pleurocystidia and observed no clamp connections in the stipitipellis. Both Vanuatu specimens contain pleurocystidia ranging from thin to thick-walled with variable apex types but lack any septate pleurocystidia.

Considering the extensive morphology within the P. albostipitatus complex, further investigation of delimiting characters is necessary, including comparisons to specimens of P. septocystidiatus . Based on the description and photo of the Korean holotype of P. septocystidiatus ( Fig. 1 , Ševčíková et al. 2014), the dark brown, striate, and centrally rugulose characters of the pileus (perhaps comparable to punctate/warted/nippled) seem to be shared characters within the observed range of comprehensive descriptions of P. albostipitatus . Previous authors have acknowledged other taxonomically useful characters when distinguishing species in sect. Pluteus including the presence of clamp connections in the pileipellis and stipitipellis tissue ( Justo et al. 2014, Singer 1956). Molecular studies of sect. Pluteus have also found the use of tef1 gene data to provide better phylogenetic resolution compared to ITS alone ( Justo et al. 2014, Menolli et al. 2014). Further study and intensive re-examination utilizing these characters and additional molecular markers could provide better resolution in the P. albostipitatus complex. For the sake of this study, identification of the Aneityum material better fits the wide range of morphological variation in P. albostipitatus . Pluteus albostipitatus appears to be a pantropical species known to occur throughout the subtropical and tropical Americas from Florida, U.S.A., through the Caribbean to Brazil and the Galapagos Islands, and tropical mainland Africa and its coastal islands. Interestingly, specimens of P. septocystidiatus have both a temperate distribution in the eastern to midwestern U.S.A. and South Korea and a subtropical to tropical occurrence in Florida, U.S.A., Vietnam, and Thailand. Although the Aneityum material is phylogenetically closer to P. septocystidiatus , the absence of septate pleurocystidia would separate them, but this septate character could just be an extension of the morphological variation within P. albostipitatus pending future studies.

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 2. Basidiome of Pluteus albostipitatus (BAP 930). Scale bar = 10 mm. Photo by: Brian Perry.

FIGURE 3. Pluteus albostipitatus. a. Basidiospores. b. Basidia. c. Basidioles. d. Pileipellis terminal elements. e. Cheilocystidia. f. Pleurocystidia. Scale bar = 10 µm. Drawings by: Jonathan del Rosario.

FIGURE 7. Basidiomes of Pluteus vanuatuensis (JAD 189 holotype). Scale bar = 10 mm. Photo by: Jonathan del Rosario.