Notes on PLUTEUS in the Pacific Northwest

Prepared for the Pacific Northwest Key Council

By Ian Gibson, South Vancouver Island Mycological Society

PLUTEUS Fr.

The Pluteus genus is characterized by small to medium fruitbody, cap convex becoming flat, dry to moist but never viscid; gills typically close and free and often wider in the middle, soft to touch, mostly white or sometimes yellowish; stem cleanly separable; veil absent; growth on wood and other substrates; spore deposit pinkish; spores smooth, nonamyloid; presence of cheilocystidia, and presence or absence of pleurocystidia and of clamp connections.

INTRODUCTION

Concepts are not yet clear enough to provide a trial Key to Pluteus species in the Pacific Northwest. No comprehensive monograph on North American species has been written although subgroups have been studied such as Section Celluloderma in North America. Limited conclusions have been drawn from molecular work, most prominently Justo et al.(2011b) on infrageneric classification and Justo et al.(2014) on Section Pluteus.

There are three traditional sections, slightly modified by Justo et al.(2011b) to accommodate molecular results. They are presented here to indicate the meaning of the terms, and to mention how the sections may correlate somewhat with the appearance of the cap. The sections will not concern us further in these Notes.

Section Pluteus: metuloid pleurocystidia, cap cuticle that is a cutis (which tends to give a smooth cap with a radial pattern of fibrils, sometimes with a tufted disc)

Section Celluloderma: non-metuloid or absent pleurocystidia, cap cuticle in most composed of short clavate or spheropenduculate cells, mixed or not with elongated cystidioid elements (which tends to give a glinty atomate look to the cap)

Section Hispidoderma: cap cuticle composed of long, elongated elements variable in size and shape, organized as a hymeniderm or trichoderm (which tends to give a velvety look to the cap, especially in the centre)

There are about 50 names on collections in herbaria around North America that come from our area (defined in these Notes as BC, WA, OR, and ID). Five are considered synonyms of other names. Four were originally described from our area - they exist here by definition, but they still may be synonyms of previously described species. Many of the others are difficult to identify, especially without a microscope. We will describe a few of the best documented Pluteus species and species groups: all of these can be recognized by appearance. After that there is a brief note on the Pacific Northwest holotypes.

DISTINCTIVE WELL DOCUMENTED SPECIES

The term “group” here implies that there are multiple named species that look similar without a microscope.

Pluteus atromarginatus (Konrad) Kühner – dark edged gills

Pluteus aurantiorugosus (Trog) Sacc. – red cap

Pluteus cervinus group (including Pluteus exilis) – very common

Pluteus cyanopus group – blue staining

Pluteus romellii group – brownish or greenish or yellowish cap; yellow stem
Pluteus tomentosulus Peck – white throughout

These taxa are the best documented Pluteus species for our area. Not coincidentally, they are the easiest to identify with macroscopic characters. The Pluteus cervinus group is the very common dark-capped mushroom with close to crowded gills and pink spore deposit, and a white stem, growing singly or in small numbers on logs. The uncommon Pluteus atromarginatus is similar but gills are dark-edged. Pluteus romellii group have brownish or greenish or yellowish caps and yellow stems and need to be distinguished from Pluteus leoninus. The rare Pluteus aurantiorugosus has a bright red to orange red cap. It is less well documented than the others but very distinctive. The rare Pluteus cyanopus group stains bluish to greenish and must be distinguished from P. salicinus. Pluteus tomentosulus is an uncommon white species and needs to be distinguished from the uncommon white variants of other Pluteus species.

Pluteus atromarginatus (Singer) Kühner black-edged Pluteus

Section Pluteus. CAP 3-12 cm across, blackish brown; at times radially streaked with blackish fibrils on a dingy background, sometimes with fine scales; moist to buttery. FLESH white. GILLS broad, close to crowded with subgills; white to pinkish, margin blackish brown. STEM 5-12 cm x 0.5-1 cm at top, equal or widening downward; whitish overlaid with dark brown fibrils. ODOR sweetish or fungoid. TASTE fungoid. HABITAT on conifer logs and debris, rarely reported from soil and deciduous woods. MICRO spores 6-9 x 4.4-5.6 um; pleurocystidia fusoid-ventricose, thick-walled, with 2-5 apical or subapical horns, cheilocystidia clavate to balloon-shaped, thin-walled, with dark brown content; cap cuticle with clamp connections.

REMARKS Pluteus cervinus group lacks the dark-edged gills and usually grows on hardwood.

Pluteus aurantiorugosus (Trog) Sacc.

Section Celluloderma. CAP 2-5.5 cm across, somewhat hygrophanous, brilliant red to orange; bald or slightly velvety and fibrillose, sometimes finely wrinkled, margin indistinctly striate. FLESH whitish to yellowish. GILLS broad, crowded to close; whitish to pinkish; edges fringed. STEM 3-6 cm x 0.3-0.1 cm, whitish to yellowish, becoming orange to red at base; striate, fibrillose to fibrillose-scaly, when mature fibrillose near base base. ODOR none. TASTE bitter. HABITAT on decayed hardwood. MICRO spores 6-7 x 4.5-5 um, pleurocystidia saccate to clavate to fusoid-ventricose with a somewhat elongated neck and obtuse apex, thin-walled, cheilocystidia mostly smaller than pleurocystidia, saccate, or clavate and with an apical nipple, or merely clavate to fusoid, or subfusoid-ventricose with a short neck and obtuse apex, thin-walled; clamp connections absent, at least from cap cuticle and trama.

REMARKS

1) P. aurantiorugosus is rare in the Pacific Northwest but spectacular.

2) It is quite closely related to P. romellii genetically. The known cap color range of the latter species ranges from brown to yellowish to greenish.

Pluteus cervinus group deer-mushroom

Section Pluteus. CAP 3-20 cm across, dark brown to pale brown to grayish brown or dingy fawn; smooth or radially fibrillose (sometimes scaly over disk), slightly viscid, often wrinkled when young, margin occasionally striate. FLESH white. GILLS broad, close or crowded, with subgills; white to pinkish, edges pallid and even but white-fringed under a hand-lens. STEM 5-19 cm x 0.3-2.5 cm, equal or widening slightly toward base; whitish or with grayish to brownish longitudinal fibrils, often spirally arranged; dry. ODOR mild to radish-like or potato-like. TASTE mild or disagreeable or earth-like or radish-like. HABITAT on decaying wood, debris, sawdust piles, or humus, usually on hardwood but can be on conifer wood. MICRO spores 5-10 x 4-6.4 um, pleurocystidia in the Pacific Northwest fusoid-ventricose, thick-walled, apices with (0-1)2-4(7) horn-like projections, cheilocystidia clavate to sphaeropedunculate to occasionally broadly fusoid, thin-walled; cap cuticle hyphae without clamp connections for Pacific Northwest group members (but see Remark 4 below).

REMARKS

1) The group is characterized by a medium to large, brown, bald cap, free, close to crowded gills without dark edges, a dingy whitish stem, typically with fine gray-brown longitudinal or spiral fibrillar striation, and growth on hardwood or the humus layer, occasionally conifer wood.

2) White forms are not rare.

3) What has been called Pluteus cervinus in the Pacific Northwest is very common, but most are Pluteus exilis, based on the molecular study of Justo et al.(2014). That molecular study designated a Pluteus cervinus clade of six species, with only Pluteus exilis definitely established for the Pacific Northwest, but P. cervinus occurring elsewhere in North America including California. Since then there is some unpublished evidence that P. cervinus also occurs in the Pacific Northwest. The species are not easy to separate from each other by appearance.

4) One of the four others in the Pluteus cervinus clade of Justo et al.(2014), Pluteus hongoi, is a possible candidate for what has been called Pluteus pellitus in the Pacific Northwest, specifically the concept without clamp connections in the cap cuticle and with relatively large spores (they would be 5.5-9.0 x 4.5-7 um for P. hongoi), larger than those given for the clamped species.

5) Pluteus atromoarginatus is similar but has dark gill edges and usually grows on conifer wood.

6) On conifer wood, Pluteus orestes and Pluteus primus need to be considered as well.

Pluteus cyanopus group

Section Celluloderma. CAP 2-4 cm across, brown; dry to moist, finely striate near margin, wrinkled-netted. FLESH white, in stem staining bluish to greenish. GILLS broad, subdistant with subgills; white then pinkish brown from spores, edge not colored. STEM 2-5 cm x 0.2-0.8 cm, fragile, equal to wider at top; gray to grayish olive near base, staining greenish gray to bluish where handled; longitudinally striate. ODOR and TASTE not distinctive. HABITAT on dead wood or wood chips. MICRO spores 6.2-8.8 x 5.3-7.5 um (P. cyanopus), 6.2-8.4 x 5.7-7.9 um (P. phaeocyanopus); pleurocystidia hornless, thin-walled, cheilocystidia numerous, many similar to pleurocystidia; cap cuticle a hymeniform layer; clamp connections absent.

REMARKS

1) In the online Species Fungorum, Pluteus cyanopus is synonymized with Pluteus chrysophaeus (Schaeff.) Quél.
2) There are at least two species in this group, Pluteus cyanopus and P. phaeocyanopus. It is unknown which species the Pacific Northwest collections labeled as P. cyanopus belong to, partly because P. phaeocyanopus was not described until 2010. Pluteus phaeocyanopus differs from P. cyanopus in that the former possesses brown pigmented gill cystidia and pleurocystidia that are more narrowly lageniform than the broadly lageniform to utriform pleurocystidia of P. cyanopus.
3) Pluteus salicinus group also stains blue. P. salicinus has a grayish brown to greenish gray or bluish gray, non-striate cap, a whitish stem that stains blue at the base, longer spores, 7-8.4(10) x 5-6 um, thick-walled, horned pleurocystidia, and a filamentous rather than cellular cap cuticle. The presence of Pluteus salicinus group in the Pacific Northwest has been questioned.

Pluteus romellii group yellow-stemmed Pluteus

A synonym for P. romellii is Pluteus lutescens

Section Celluloderma. CAP 1.5-6 cm across, brownish to greenish or (especially at margin) yellowish; dry to moist, bald (but typically appearing velvety), sometimes wrinkled at center, not obviously striate. FLESH white or pale yellow. GILLS broad, fairly close; whitish to pale yellow, finally pinkish. STEM 2-9 cm x 0.2-1.0 cm, pale yellow, the base usually brighter yellow or orange; moist to dry, bald except at very base, longitudinally striate. ODOR and TASTE mild. HABITAT on rotting hardwood logs, sticks and debris, sometimes on soil. MICRO spores 5.7-7 x 5.3-7 um; pleurocystidia lageniform to utriform, thin-walled, 28-76 x 15-35 um, cheilocystidia present, thin-walled; cap cuticle hymeniform; clamp connections absent.
REMARKS
1) Pluteus rugosidiscus is not easy to distinguish by appearance from the green-capped variant of Pluteus romellii found at least in California; as a result it could be included in the Pluteus romellii group even though not closely related. Pluteus rugosidiscus is apparently closely related to but distinct from Pluteus chrysophlebius and it has been synonymized with P. chrysophlebius in the past. Minnis et al.(2010) say that the pleurocystidia of P. chrysophlebius (and P. rugosidiscus which they synonymize) are lageniform, 44-67 x 12-22 um, and not of the broad type found in P. fulvobadius (see below) and P. romellii. Spore size of P. chrysophlebius is similar at 5.3-7.9 x 4.8-7 um. A collection on soil is likely not to be P. rugosidiscus.
2) Pluteus fulvobadius is a controversial species, but Minnis et al.(2010) say the names Pluteus romellii and P. lutescens have been misapplied to this species in western North America. It is therefore included in the P. romellii group.
3) Pluteus leoninus may have a yellowish stem as well and can be very similar. It has a velvety plush cap when young and is often brighter yellow capped. Because of the velvety plush surface (Section Hispidoderma as opposed to Section Celluloderma for the other species discussed above), it is excluded here from the P. romellii group, even though Homola (1972) says that P. lutescens in the western United States typically appears somewhat granulose to velvety.

Pluteus tomentosulus Peck small white deer-mushroom
Section Celluloderma. CAP 2.5-10 cm across, whitish become tinged pinkish along margin and yellowish over disc; dry, cottony to woolly. FLESH white. GILLS broad, crowded; white then pinkish. STEM 5-11 cm x 0.4-1 cm, equal, often with a slight bulb; white, upper part pinkish when old and base often yellowish; pruinose to densely pubescent overall at first, more or less appressed-fibrillose near base when old and longitudinally striate in upper part. ODOR and TASTE not distinctive. HABITAT on wood. MICRO spores 5-7 x 4.5-6 microns; pleurocystidia fusoid-ventricose, thin-walled, lacking horns, cheilocystidia similar to pleurocystidia; clamp connections absent.
REMARKS
1. Several other species of Pluteus have white or pale variants including the Pluteus cervinus group. Attention should be paid to following characters of P. tomentosulus: a) the cottony to woolly surface, b) (usually) the absence of any brown color or streaks, and c) (often) the presence of a bulb.
2. Pluteus pellitus has been reported from the Pacific Northwest. P. pellitus has a smoother cap and stem, often with some brown coloring, horned pleurocystidia, and clamp connections.The reports could instead represent Pluteus nothopellitus, described afterl some collections were deposited, also with a smoother cap and stem, often with some brown coloring, and with horned pleurocystidia but with larger spores than P. tomentosulus, and lacking clamp connections.

SPECIES WITH HOLOTYPES FROM OUR AREA

Pluteus fulvobadius Murrill holotype from OR

Pluteus heterocystis P. Banerjee & Sundb. holotype from WA

Pluteus latifolius Murrill holotype from WA

Pluteus washingtonensis Murrill holotype from WA

Pluteus fulvobadius is a controversial species. Banerjee & Sundberg (1993b) considered it was probably not a Pluteus at all. Minnis et al.(2010), also with Sundberg as co-author, considered instead to be the correct name for what has been considered to be Pluteus romelli (or Pluteus lutescens) in the Pacific Northwest.

Pluteus heterocystis was described from A.H. Smith’s unpublished notes about a single collection that was re-examined. Justo et al.(2014) considered Pluteus heterocystis a doubtful name, likely representing Pluteus brunneidiscus as they describe it.

Pluteus latifolius is known chiefly from microscopic examination of the original holotype which is in poor condition. A potentially distinctive feature is microscopic: pleurocystidia that have an apical to subapical appendage.

Pluteus washingtonensis is synonymized by Justo & Castro(2007a) with Pluteus brunneidiscus.

REFERENCES

1. Arora, David. 1986. Mushrooms Demystified Second Edition. Ten Speed Press, Berkeley.

2. Banerjee, Partha, Walter J. Sundberg. 1993a. “Three New Species and a New Variety of Pluteus from the United States.” Mycotaxon 47: 389-394.

3. Banerjee, Partha, Walter J. Sundberg. 1993b. “Reexamination of Pluteus Type Specimens: Types Housed at the New York Botanical Garden.” Mycotaxon 49: 413-435.

4. Banerjee, Partha, Walter J. Sundberg. 1995. “The genus Pluteus (Pluteaceae, Agaricales) in the Midwestern United States.” Mycotaxon 53: 189-246.

5. Homola, R.L. 1972. “Section Celluloderma of the genus Pluteus in North America.” Mycologia 64(6): 1211-1247.

6. Justo, A., M.L. Castro. 2007a. “Observations in Pluteus section Pluteus in Spain: two new records for Europe.” Mycotaxon 102: 209-220.

7. Justo, A., M.L. Castro. 2007b. “Pluteus nothopellitus sp. nov. and a review of white species in Pluteus section Pluteus.” Mycotaxon 102: 221-230.

8. Justo, Alfredo, Andrew M. Minnis, Stefano Ghighone, Nelson Menolli Jr., Marina Capelari, Olivia Rodríguez, Ekaterina Malysheva, Marco Contu, Alfredo Vizzini. 2011a. “Species recognition in Pluteus and Volvopluteus (Pluteaceae, Agaricales): morphology, geography and phylogeny.” Mycol. Progress 10: 453-479.

9. Justo, Alfredo, Alfredo Vizzini, Andrew M. Minnis, Nelson Menolli Jr., Marina Capelari, Olivia Rodríguez, Ekaterina Malysheva, Marco Contu, Stefano Ghighone, David S. Hibbett. 2011b. “Phylogeny of the Pluteaceae (Agaricales, Basidiomycota): taxonomy and character evolution.” Fungal Biology (Oxford) 115(1): 1-20.

10. Justo, Alfredo, Ekaterina Malysheva, Tatiana Bulyonkova, Else C. Vellinga, Gerry Cobian, Nhu Nguyen, Andrew M. Minnis & David S. Hibbett. 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.

11. Miller Jr., Orson K., Hope H. Miller. 2006. North American Mushrooms. A field guide to edible and inedible fungi. Falcon Guide.

12. Minnis, Andrew M., and Walter Sundberg. 2010. “Pluteus section Celluloderma in the U.S.A." North American Fungi 5(1): 1-107.

13. Siegel, Noah, and Christian Schwarz. 2016. Mushrooms of the Redwood Coast - A Comprensive Guide to the Fungi of Coastal North California. Ten Speed Press. Berkeley.

14. Singer Rolf. 1956. “Contributions towards a monograph of the genus Pluteus”. Trans. Brit. Mycol. Soc. 39: 145-232.

15. Smith, Alexander H., Daniel E. Stuntz. 1958. “Studies on the Genus Pluteus I. Redescriptions of American Species Based on a Study of Type Specimens.” Lloydia 21:(3) 115-136.

16. Smith, Alexander H., Daniel E. Stuntz. “Studies on the Genus Pluteus II. “ Unpublished.

17. Trudell, Steve, Joe Ammirati. 2009. Mushrooms of the Pacific Northwest. Timber Press.