Pluteus aff. argentinensis 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 : 78-82

Pluteus aff. argentinensis Singer, Lloydia 21: 230 (1958) ( Figs. 38 , 39 )

Diagnosis:— Pluteus aff. argentinensis from Tanna is characterized by a pileus with a fuliginous longitudinally-striate fibrillose surface and dark gray disc surface, and a gray longitudinally-striate fibrillose stipe with basal tan floccules. Microcharacters include subglobose basidiospores (6.4 × 6.1 µm), fusoid-ventricose cheilocystidia and pleurocystidia sometimes covered apically or entirely with mucilage, a cutis pileipellis with suberect dark brown pigmented fusoid terminal elements, and an absence of caulocystidia and clamp connections.

Description:— Pileus 55–75 mm diam., convex expanding to plano-convex with a slight to deep (8–10 mm) central depression, margin slightly sulcate, eroded; surface pellucid-striate towards margin, dull elsewhere, dry, strongly longitudinally appressed-fibrillose or silky; fibrils fuliginous to ash brown (oac624–oac627) densest and darkest at disc fading towards margin, underlying surface pallid tan. Context up to 2 mm thick, colored pallid tan (oac661–oac662). Lamellae free, crowded with 3–4 tiers of lamellulae, thin, white to cream-white. Stipe 52–80 × 5–8 mm, central, terete, cylindrical sometimes arising from a white tomentum, hollow; surface pearlescent, dry, silky, off-white to gray overall, context off-white. Odor indistinct. Taste indistinct.

Basidiospores 5–7 (–8) × 5–7 µm, [x mr = 6.36–6.5 × 6.02–6.18 µm, x mm = 6.43 ± 0.09 × 6.1 ± 0.11 µm, Q = 1–1.2, Q mr =1.05–1.06, Q mm = 1.05 ± 0.01, n = 50, s = 2], globose to subglobose, smooth, hyaline, with a guttule, inamyloid, thick-walled. Basidia 24–38 (–50) × 6–10 µm, clavate to cylindro-clavate, 4-spored, hyaline, guttulate, thin-walled, sterigmata 2–4 × 0.5–1 µm. Basidioles 20–25 × 5–8 µm, clavate, hyaline, guttulate, thin-walled. Lamellar edge sterile. Cheilocystidia 25–80 × 10–24 µm, clavate to broadly clavate or fusoid-ventricose to narrowly utriform, obtuse or rarely umbonate, often with apical mucilage sometimes adhering spores that obscure view, hyaline, thin-walled. Pleurocystidia 42–100 (–140) × 12–42 (–50) µm, scattered, broadly clavate to fusoid-ventricose, narrowly lageniform, or sometimes broadly sphaeropedunculate, obtuse, some with apical or completely enveloped in mucilage sometimes with adhering spores that obscure view, hyaline, thin-walled. Pileipellis a cutis of repent hyphae, composed of dark brown plasmatic pigment or hyaline, non-incrusted, non-gelatinous, thin-walled, cylindrical hyphae, 4–16 µm diam.; terminal elements 40–90 (–155) × 8–20 (–35) µm, mostly repent becoming suberect in fascicles especially at the disc, cylindro-clavate to fusiform, obtuse or seldom subcapitate. Pileus trama interwoven, composed of hyaline, non-gelatinous, thin-walled, clavate to inflated hyphae, 4–22 µm diam.. Lamellar trama inverse, composed of hyaline, non-gelatinous, thin-walled hyphae, 5–16 µm diam.. Stipitipellis a cutis, composed of hyaline or infrequently with pale brown plasmatic pigment, non-incrusted, non-gelatinous, thin-walled hyphae, 8–16 µm diam.. Caulocystidia absent. 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 ) 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, Yanemari , 19°28.511′S, 169°25.616′E, elev. 146 m, 30 August 2018, coll. J. A . del Rosario, JAD 171 ( HAY); Tanna, Port Resolution near Tanna Horizon Bungalow , 19°31.391′S, 169°30.371′E, elev. 7 m, 16 August 2019, coll. J. A . del Rosario , M . Wahe & G. M . Plunkett , JAD 301 ( HAY) .

Notes:— Pluteus argentinensis Singer (1958: 230) was originally described by Singer based on two collections from Argentina, one (Singer T 929) was initially identified as P. plautus ( Singer & Digilio 1952) and the other (Singer T 2139) was designated as the holotype ( Singer 1958). Since then, P. argentinensis has been reported from Mexico ( Rodríguez & Guzmán-Dávalos 1999, 2001) and Brazil ( Dias & Cortez 2013). According to Dias and Cortez, a report by Wright and Albertó (2002) from Buenos Aires may be misidentified based on the presence of clamp connections in that material.

The Vanuatu specimens fit well within previous descriptions of P. argentinensis , however there are some discrepancies. Macroscopically, the Vanuatu material matches the holotype description, except that the pileus size is significantly larger than the type (25–35 mm diam.) and slightly larger compared to the other reports. In the original description, Singer described the pleurocystidia and cheilocystidia together by generalizing the size as “34–68 × 14–25 µm, mostly 42–54 × 14–19 µm” and shape “ventricose below and ampullaceous or mucronate above”, and differentiated the cystidia on the lamellar edge by “some ventricose-vesiculose or ampullaceous-subcapitate” ( Singer 1958). Singer also observed the presence of an inconspicuous resinous incrustation on these cystidia. Both lamellar cystidia in the Vanuatu material fit these criteria, except for being slightly larger. The presence of any type of incrustation/mucilage on cystidia was not reported from either the Mexican or the Brazilian material ( Rodríguez & Guzmán-Dávalos 1999, 2001, Dias & Cortez 2013). Compared to the Vanuatu collections, the Mexican material would be closer in pleurocystidia and cheilocystidia shape variety ( Rodríguez & Guzmán-Dávalos 1999), while the Brazilian material is similar in size, but the pleurocystidia were described only as ventricose and lack lageniform or clavate elements ( Dias & Cortez 2013). The orientation of the pileipellis is not clearly categorized in the original description of P. argentinensis , and Singer only provided measurements, an illustration and emphasized the terminal elements as “fusoid to ventricose with strongly attenuate apex” ( Singer 1958). Singer’s collection T 929, originally identified as P. plautus , described the pileipellis as a trichoderm with the majority of the elements depressed ( Singer & Digilio 1952). Pileipellis interpretation has varied in concepts of P. argentinensis as Rodríguez and Guzmán-Dávalos (1999) described their material as a trichoderm and suberect, while Dias and Cortez described “filamentous and elongated hyphae” providing a photo similar to a repent cutis with terminal elements appearing as ascending ( Fig. 4 , Dias & Cortez 2013). Rodríguez and Guzmán-Dávalos did re-examine a portion of the holotype, but due to the poor condition of the material were unable to measure elements of the pileipellis and could only provide spore measurements ( Rodríguez & Guzmán-Dávalos 2001). Singer placed P. argentinensis in his morphological stirps Fuliginosus , which he characterized by the pileipellis terminal cells being subacute or acuminate-subacute and part of a trichoderm ( Singer 1958, 1986). Regarding the Vanuatu material, the pileipellis is overall a cutis with the terminal elements sometimes turning to erect clusters with the shape and size of the terminal elements fitting well with all previous described material, but the ambiguity of the pileipellis arrangement from the protologue requires clarity. Singer did not originally describe the shape of the spores, but the Vanuatu material matches in size and matches the shape and size in the other material. The absence of caulocystidia was noted in the Mexican material ( Rodríguez & Guzmán-Dávalos 1999), but other authors omitted its presence or absence. Overall, the Vanuatu specimen’s pleurocystidia and cheilocystidia closely resemble those in the Mexican material, while the Brazilian material lacks clavate cystidia. Both the Mexican and Brazilian material lack mucilage/ incrustation on their cystidia, but this character is shared with the holotype according to the original description. Interestingly, the accompanying picture of the Brazilian specimen bears a resemblance to the Vanuatu material ( Fig. 1 , Dias & Cortez 2013), and the pileipellis shares some similarity as well. The slight difference in cystidia shape from the Brazilian material may be just minor variation and both might be the same species, but molecular data is unavailable for further confirmation. Regardless, clarification of pileipellis arrangement and molecular sampling would be preferred to confirm this material as P. argentinensis . Observations of the presence of mucilage/incrustation and the arrangement of the pileipellis in the other material would also be necessary to confirm their identities and strengthen the concept of P. argentinensis . In agreement with Menolli and Capelari (2016), a revision of the holotype is necessary to refine the concept of P. argentinensis and ideally a re-examination of these collections would unite them.

A number of species from Singer’s morphological stirps ( Singer 1986), such as Diptychocystis , Fuliginosus , or Spilopus , resemble the Vanuatu specimens, but their micromorphological characters can subtly distinguish them. Pluteus diptychocystis Singer (1954: 123) was described from Argentina ( Singer 1954) and has been reported from Chile ( Singer 1969) and Brazil ( Menolli & Capelari 2016). Macromorphologically, P. diptychocystis differs in having a tomentose to squamulose pileus and micromorphologically differs by having slightly larger ellipsoid spores (6.8– 9.6 × 5.3–7 µm), more lageniform or “ampullaceous with broad neck” and less cylindro-clavate pleurocystidia and cheilocystidia, and more apically rounded pileipellis terminal elements ( Singer 1954, 1956, 1958, Menolli & Capelari 2016). Pluteus striatocystis Pegler (1977: 268) was originally described from east Africa ( Pegler 1977) and reported from re-identified material from Brazil ( Menolli et al. 2015a). This species primarily differs micromorphologically with more ellipsoid spores, smaller pleurocystidia (40–70 × 15–25 µm) with a characteristic distinct striate collar, smaller cheilocystidia (36–46 × 11.2–20 µm) absent of mucilage/incrustation, and longer pileipellis terminal elements (–214 × 17.5 µm) ( Pegler 1977, Menolli et al. 2015a). The Bolivian P. pluvialis Singer (1958: 234) may be interpreted as similar by sharing a pubescent “margined” bulbous base, although the Vanuatu material here is described as cylindrical with a white tomentum ( Singer 1958). Regardless, P. pluvialis would differ through being smaller in stature, having granular punctations on the pileus, slightly smaller cheilocystidia (40–55 × 7–21 µm), smaller pleurocystidia, and larger pileipellis elements (82–165 × 16.5–19.5 µm) with more attenuate apices.

Pluteus cubensis (Murrill) Dennis (1953: 155) is a morphologically variable species distributed throughout the tropical Americas ( Murrill 1911, Dennis 1953, Singer 1956, 1958, Pegler 1983, 1997, Menolli et al. 2015a). Phylogenetic analysis of ITS data ( Fig. 37e ) places the Vanuatu P. aff. argentinensis in a well-supported sister relationship (BS 100 %, PP 1.0) to a Brazilian specimen of P. cubensis ( HM562161 ). A recent re-examination of the type specimen of P. cubensis by Menolli et al. (2015a) resulted only in the measurement of two cheilocystidia and ellipsoid basidiospores, and they were unable to report the presence of granular incrustation or nodulose excrescences that were observed by Singer ( Singer 1956, 1958).A survey of the literature of P. cubensis leaves it uncertain if Singer’s cystidia incrustation observations should be included in the current concept of this species, and its absence may be taxonomically informative. Therefore, P. cubensis can be distinguished from the Vanuatu specimen in having more ellipsoid basidiospores, smaller pleurocystidia (43–55 [–77] × ([12.5–] 13.7–20 [–22] µm), smaller cheilocystidia ([20–] 31–47 [–56] × [8.7–] 10.0–21 [–25]) lacking mucilage/incrustation, and more rounded to obtuse pileipellis terminal elements ( Singer 1956, 1958, Pegler 1983a, Menolli et al. 2015a). The two taxa are phylogenetically placed on a branch sister to P. brunneosquamulosus Pradeep & Vrinda (2012: 870) and P. eliae Singer (1958: 290) , but this is unsupported. The Indian P. brunneosquamulosus and Bolivian P. eliae are completely different from the Vanuatu specimen due to paler brown, non-fuliginous basidiomes and an epithelioid or hymeniderm type pileipellis ( Pradeep et al. 2012; Singer 1958).

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 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 38. Basidiomes of Pluteus aff. argentinensis (JAD 301). Scale bar = 10 mm. Photos by: Brian Perry.

FIGURE 39. Pluteus aff. argentinensis. a. Basidiospores. b. Basidia. c. Basidioles. d. Pileipellis terminal elements. e. Cheilocystidia. f. Pleurocystidia. Scale bar = 10 µm. Drawings by: Jonathan del Rosario.