Yellow *Pluteus* and the chryso-complex

On several occasions I have observed pluteoid basidiomes with dark yellow-brown to yellow pilei and whitish stipes, fruiting around the same well-rotted stump of a deciduous tree in semi-ancient mixed deciduous woodland. Genus of wood unknown.

Initially, I wanted to say these were Pluteus chrysophaeus, but then I read that some authors consider this a synonym of Pluteus chrysophlebius. So, I had to investigate a bit more.

https://www.inaturalist.org/observations/175925918
https://www.inaturalist.org/observations/186412237

The genus:

• Pluteus is a classical genus described by Fries in 1836 and is typified by P. cervinus, which was originally described by Schaeffer from Germany in 1774.
• Quite large, estimated to contain over 300 species, grouped into three sections, which also have various historical subsections.
• Worldwide distribution, and some species appear to have inter-continental ranges.
• Saprotrophic on wood, generally preferring well-rotted wood, the spore deposit is ‘pink’ to buff, there is no ring or other remnants from a veil, and the gills are broad, free, and crowded.
• The spores are generally smooth and round to ellipsoid, often with large guttales (vacuoles).
• Common names include ‘Shields’ and ‘Deer Mushrooms’.
• Some species are reported to be edible but not choice, and others to have low levels of psychoactive toxins like psilocybin.

Yellow species:

• Specimens with gold, yellow, yellow-brown, or greenish-yellow colours are now usually classified into four species:

1. P. leoninus (Shaeff., 1774) P. Kumm. (1871), described from Germany.
2. P. chrysophaeus (Schaeff., 1774) Quel. (1872), described at the same time as P. leoninus from Germany.
3. P. chrysophlebius (Berk. & Ravanel, 1859) Sacc. (1887), described from South Carolina, North America. [Sometimes still called P. admirabilis (Peck, 1872) Peck (1885) in the US, although widely synonymised in the literature after Smith (1956)].
4. P. rugosidiscus Murrill (1917), described from New York, North America.

• P. leoninus is in section Hispidioderma, and it can be distinguished by microscopic characters (pileipellis a trichoderm) and sometimes on macroscopic characters (pileus colour and texture, and basidiome stature).
• The other three species are in section Celluloderma (hymeniderm of short elements), and also within the same clade in the section (this clade has no reported morphological distinctions).

Problems circumscribing species in the chrysophaeus/phlebophorus-clade:

• There has traditionally been considerable confusion about P. chrysophaeus and the closely related P. phlebophorus (Ditmar, 1813) P. Kumm. (1871). There are no type specimens for either of these concepts, and the original descriptions are brief and lack any modern (or microscopic) characters.
• P. phlebophorus is usually taken to have a browner pileus (and often more venose) like the illustration given with the protologue.
• P. chrysophaeus is originally described by Schaeffer as having ‘gold-saturated’ pileus, and the specific epithet translates to ‘dusky-gold’.
• The illustration of P. chrysophaeus (now designated lectotype by Justo et al., 2011a), appears to show an immature basidiocarp with a brownish-yellow pileus.
• To complicate matters further, later descriptions by Fries, Quelet (1872), and Saccardo (1887), describe the colour as ‘dark cinnamon’ or ‘brownish’.
• Vellinga (1990) presents a more detailed morphological concept for P. chrysophaeus in Europe that includes microscopic characters. She describes the pileus as olive-yellow when moist and yellowish-ochraceous brown, and also includes greenish-yellow in her key.
• Vellinga describes the micromorphology of P. chrysophaeus as variable and synonymises the three concepts of Orton (1960): P. galeroides, P. luteovirens, and P. xanthophaeus.
• Vellinga comments that her description (based on collections from NL, UK, and GER) is a good fit for Schaeffer’s protologue, although she does not give his illustration as a selected icon.
• As a result of the confusion over the lectotype and the more brown description of the pileus in some historic descriptions, several authors (Smith, 1956; Orton, 1960; and Kibby, Burnham & Henrici, 2010) suggest that P. chrysophaeus is widely synonymous with P. phlebophorus and any other sense of the name should be abandoned due to confusion.
• Kibby, Burnham and Henrici (2010) also suggest that another name from Orton, like P. luteovirens, could be revived if necessary.
• Although it is not discussed in the literature, there is a noticeable difference in the stated proportions of basidiomes given in description of Saccardo (1887) compared to Vellinga (1990), which also encourages me to think that later authors may have confused Schaeffer’s species with others in the C/P clade or even other clades.
• Minnis and Sundberg (2010) share the view that P. chrysophaeus is confused, and suggest P. chrysophaeus sensu Vellinga (1990) and P. rugqosidiscus are synonymous under P. chrysophlebius, reporting no distinguishing morphological differences.

More recent work:

• Justo et al., (2011a) present a phylogeny for Pluteus based on ITS, and Justo et al., (2011b) extend this to consider nSSU and nLSU.
• These phylogenies support the traditional sections (with some exceptional species moved to Celluloderma), but the organisation of sections into natural subsections is not clear.
• Within section Celluloderma, the chrysophaeus/phlebophorus (C/P) clade seems to have significant support and includes the collections identified as P. phlebophorus, P. chrysophaeus, P. chrysophlebius, and P. rugosidiscus (and their accepted synonymies).
• Sevcikova and Bovrika (2019) present a wider ITS-based phylogeny of the C/P clade and a few observations of differences in other genes.
• Both P. phlebophorus and P. rugosidiscus seem to have more distinct positions compared to the other species in the C/P clade, and P. phlebophorus is generally associated to a distinct and distinguishable species.
• Notably the holotypes for P. chrysophlebius and P. rugosidiscus have not been sequenced, and no type specimens have been designated for those without one
• Justo et al. (2011a) continue with the idea that P. chrysophaeus sensu Vellinga (1990) is synonymous with P. chrysophlebius, describing an intercontinental species, and reporting that the inter-continental variation in ITS is less than 2%.
• Collections in the chryophaeus/chrysophlebius (C) subclade, or complex, form geographical clades, and the sample size in Justo et al. (2011a) does not seem significant enough to determine the variance. Sevcikova and Bovrika (2019) also seem to disagree that the matter is settled.
• In much of the criticism of P. chrysophaeus there is a lot of focus on the perceived mismatch between the (designated) lecotype and the protologue.
• In my view, the protologue and specific epithet should have priority over the illustration, and regardless, the illustration still fits within the description and seems to correspond to collections from Europe and North America (even if it may not be best single specimen for identification).
• The specimens from the C complex that I have observed had brownish immature pilei and yellow mature pilei in the same group. This is also reported by Sevcikova and Bovrika (2019) in Europe and Micheal Kuo in North America (in the description of P. chrysophlebius on his website).
• I would be reluctant to abandon Schaeffer’s name (which has been used for many years in Europe and Asia), based on the potential criticisms of the lectotype, and the synonymy of later descriptions with brown species. P. chrysophaeus is the youngest name in the clade and would also have priority over P. chrysophlebius in a synonymy.
• P. rugosidiscus has recently been found in Europe for the first time, reported in Sevcikova and Bovrika (2019), and a more detailed ITS-based phylogeny of the C/P clade still supports a separate but cryptic species.
• This species is said to be characterised by green colours in the pileus, although Vellinga (1990) includes greenish-yellow in her key to P. chrysophaeus, and Sevcikova and Bovrika (2019) conclude that this is not a distinguishing feature based on ITS.
• Sevcikova and Bovrika (2019) question some of the historic synonymies in the C complex, on the basis of morphology, and suggest that more work is needed to decide on some of Orton’s concepts (1960).
• No clades for these species are represented in the current phylogenies but the variability of the groups on the C/P clade suggests careful analysis of molecular data to obtain a significant understand of the relationships.
Conclusion:
• Section Celluloderma requires more molecular data across more species to achieve a clearer understanding of the relationships between the clades.
• Biological/mating studies for the different clades would be helpful.
• For the C complex, without more molecular data across more collections (including the holotype of P chrysophlebius), it seems difficult to decide whether there are one or more species (e.g. North American and European/Asian) or even some that have not been sequenced.
• Unless future morphological studies can determine more distinguishing characters, then the species in the C complex would appear to be cryptic - only distinguished by molecular data or geography.
• Recent results suggest P. rugosidiscus could represent another cryptic species in the C/P clade, which can only be reliably distinguished by ITS.

References:

Bas, C., Kuyper, T., Noordeloos, M., Vellinga, E., Boekhout, T. & Arnolds, E. (1990). FLORA AGARICINA NEERLANDICA: Critical monographs on families of agarics and boleti occurring in the Netherlands, vol. 2.
Justo, A., Minnis, A.M., Ghignone, S. et al. (2011a). Species recognition in Pluteus and Volvopluteus (Pluteaceae, Agaricales): morphology, geography and phylogeny. Mycol Progress 10, 453–479.
Alfredo Justo, Alfredo Vizzini, Andrew M. Minnis, et al. (2011b). Phylogeny of the Pluteaceae (Agaricales, Basidiomycota): taxonomy and character evolution. Fungal Biology, 115(1), 1-20.
Justo, A., Malysheva, E., Bulyonkova, T. et al. (2014). Molecular phylogeny and phylogeography of Holarctic species of Pluteus section Pluteus (Agaricales: Pluteaceae), with description of twelve new species. Phytotaxa, 180(1), 1-85.
Geoffrey Kibby, Antony Burnham, Alick Henrici, (2010). Some problems in the genus Pluteus, Field Mycology, 11(3), 93-100.
Minnis, A. M., & Sundberg, W. J. (2010). Pluteus section Celluloderma in the USA. North American Fungi, 5, 1-107.
Nelson Menolli Jr. , Tatiane Asai & Marina Capelari (2010). Records and new species of Pluteus from Brazil based on morphological and molecular data, Mycology, 1:2, 130-153, DOI: 10.1080/21501203.2010.493531
Orton, P.D. (1960). New check list of British Agarics and Boleti: part III. Notes on genera and species in the list. Trans. Brit. Mycol. Soc. 43 (2): 359–360.
Ševčíková, Hana; Bororvička, Jan (2019). Pluteus rugosidiscus (Basidiomycota, Pluteaceae), first record of this North American species in Europe. Nova Hedwigia, 108(1), 227–241.
Ševčíková H, Malysheva E, Ferisin G, Dovana F, Horak E, Kalichman J, Kaygusuz O, Lebeuf R, González GM, Minnis AM, et al. Holarctic Species in the Pluteus romellii Clade. Five New Species Described and Old Names Reassessed. Journal of Fungi. 2022; 8(8):773.

Posted on 2023년 11월 23일, 23시 20분 12초 UTC by shelbourne