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Russula parvovirescens sp. nov., a common but ignored species in the eastern United States

     Muséum national d’histoire naturelle, Systematics and Evolution Department, UMS 602–Post Box 39, 75231 Paris Cedex 05, France

Donna Mitchell

     WV DNR Wildlife Diversity Program, PO Box 67, Ward Road, Elkins, West Virginia 26241

Jeri Parrent

     Department of Biology, Duke University, Biological Sciences Building Room 139, Durham, North Carolina 27708

	ABSTRACT

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Russula parvovirescens sp. nov. is described from the eastern United States. It is a rather common species that previously was mistaken for a small R. virescens or a green form of R. crustosa. The large and characteristic extremities that compose the pileipellis allow easy identification with the microscope or even with a good hand lens. The new species is described here, illustrated in detail and compared with R.virescens and R. crustosa.

Key words: North America, Russulaceae, taxonomy

	INTRODUCTION

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Russula is one of the more common genera among the larger, gilled mushrooms in the United States (US) and in the rest of the world. Yet few American mycologists have developed an active interest in this colorful genus. With the death of Raymond Fatto at the end of 2002, North America lost its most important local expert on eastern US russulas. The apparent lack of interest in Russula in this part of the world, at least when compared to Europe, is surprising because most of the early descriptive work on American russulas originated from that area through the work of C. Peck, G. Burlingham and W. Murrill. Between the end of the 19th century and the mid-20th century, these mycologists described most of the presently known species of Russula in the US. And during the past 50 y nearly all the new taxa of American Russula described by R. Singer, R. Shaffer, G. Bills or R.M. Fatto were essentially eastern species (annotated references for the complete American Russula literature can be consulted at http://www.mtsn.tn.it/russulales-news/lt_search.asp).

A total of 330 Russula species have been described from the United States, according to our records, and an additional 87 European taxa have been reported to occur in the US as well. An online key to these species, adapted from a synoptic key (Kibby and Fatto 1990) that had been limited to eastern taxa, can be accessed at http://www.mtsn.tn.it/russulales-news/id_kibby_fatto.asp. (For an online key to exclusively western taxa [Woo 1989] see http://www.svims.ca/council/Russul.htm). The usefulness of these keys is still not satisfactory. A large number of seemingly common taxa in the US still remain to be described (Buyck and Mitchell 2003, Buyck 2004), while most of the described taxa are in need of a modern revision.

In this contribution we present the description of R. parvovirescens sp. nov., a small Russula which has previously been mistaken by local mycologists for either R. crustosa Peck or R. virescens (Schaeff.) Fr. It is quite common along the east coast of the United States, and also might be present along the Gulf of Mexico coast. Microscopic examination reveals a morphologically well characterized species that easily can be separated from both of the aforementioned taxa. Molecular phylogenetic analysis show that these specimens form a well supported clade closely related to R. crustosa and R. virescens (Buyck et al 2005).

	MATERIALS AND METHODS

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The majority of the studied material was obtained through herbarium loans from NYBG and DEWV, misidentified as R. crustosa or R. virescens. Additional specimens collected by G. Boyd (New Jersey), D. Lewis (Texas), D. Mitchell (West Virginia) and R. Vilgalys (North Carolina) as well as by the senior author also were included in this study. Comparative type material for the above taxa as well as for some other mild green russulas was borrowed from TENN, NYS and NYBG. Description of macroscopic characters and comments on their variation are mainly based on notes and photographs accompanying some recent specimens collected by D. Mitchell and the senior author. Color references for the fungi follow Kornerup and Wanscher (1978) and refer to the widely used codes introduced by Romagnesi (1967) and Dagron (unpublished) for spore print color. Microscopic features were examined and sketched by B. Buyck. All microscopic observations and measurements were made in ammoniacal Congo red, after a short aqueous KOH pretreatment to improve tissue dissociation and gelatinous matrix dissolution. Original drawings for all elements of the hymenium or pellis were made at 2600x with a drawing tube. All tissues also were examined for the presence of ortho- or metachromatic contents or incrustations in cresyl blue as explained in Buyck (1989). Field pictures of the new taxon are posted at http://www.mtsn.tn.it/russulales-news/tx_photos.asp?index=7373.

Spore measurements were performed in Melzer’s reagent and are based on 20 spores per specimen. Intervals for mean spore length and width among measured collections are indicated in italic with "n" indicating the total number of spores measured for the taxon. Spore size variation gives the variation of the mean spore length and width among the measured collections accompanied, between brackets, by substracted and added doubled standard deviation. In the same way, the amplitude of the mean values for the length/width ratio (Q) calculated for every measured collection is indicated, but preceded, respectively followed, by the lowest, respectively highest, measured value for Q. Cystidial terminology follows Buyck (1991).

	RESULTS

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Russula parvovirescens spec. nov. FIGS. 1–9

View larger version (29K): [in this window] [in a new window]   FIGS. 1–7. Russula parvovirescens. (all from holotype unless indicated otherwise) 1. Basidia and basidiola. 2. Pleurocystidia with contents as observed in Congo red in two elements, schematically in the others. 3. Spores. 4. Spores (DEWV 4811). 5. Spores (DEWV 4503). 6. Marginal cells. 7. Cheilocystidia. Bar = 5 µm for spores, 10 µm for other elements.

View larger version (21K): [in this window] [in a new window]   FIGS. 8–9. Russula parvovirescens (holotype). 8. Pileocystidia with contents represented schematically. 9. Hyphal terminations composing the suprapellis pseudoparenchyma. Bar = 10 µm.

Cap 40–60(80) mm diam, quite regular in form, slightly depressed to plane in the center, toward the margin rather thin and slightly striate with age; surface feltyvelutinous, dull, never viscous; suprapellis separable for one-half to one-third of the radius, greenish brown to dark olive green or metallic bluish green, rapidly becoming coarsely disrupted forming typically large pellicles exposing the grayish to bluish green or pale brownish gray fibrous flesh of the subpellis, developing ferruginous discolorations upon exposure, often entirely discoloring pale brown in the center, at other times remaining much darker in the center; the appressed pellicles often turning paler than the surrounding context because of the presence of a pale reticulate pattern easily observed with a hand lens. Gills adnate to subfree, 4–8 mm high, slightly narrowing towards the cap margin, more or less 1/mm, brittle, locally anastomosing to forking around the stipe, some forking closer to the cap margin, not interveined, cream; edges concolorous, even. Stipe 30–62 x 8–13 mm, slender, not hard-fleshed, smooth, cylindrical, longer than the cap diameter, not pruinose, whitish, rounded at the base, the interior with a few cavities; veil absent. Flesh 4–5 mm thick above the gill attachment to the stipe, mild, inodorous, white, turning brownish orange with FeSO4 on stipe context, but only slightly discoloring on stipe surface, moderate to strong reaction with guaiac. Spore print pale cream (Romagnesi IIa, Dagron 3–4). Exsiccatum with dark green (4F4–8) to grayish green (3E3–5) to olive green (4DE3–5) or exceptionally reddish brown (6–7DE5–7), sometimes decolored and pale brown (5CD5–7) in the center, cap surface strongly fissured and exposed flesh much paler (3–4B3–4). Stipe and gills not colored.

Spores 6.7–7.5–8.0–9.1 x 5.7–6.4–6.5–7.2 µm, Q = 1.07–1.17–1.26–1.43 (n = 80); ornamentation a dense to moderately dense incomplete network of often interconnected obtuse warts and short crests, strongly amyloid, less than 1 µm high, suprahilar plage either nonamyloid or with a weakly amyloid spot or amyloid verruculae, some collections with a clear amyloid spot on most spores. Basidia 38–45 x 8–9 µm, inflated in upper half, 4-spored, rarely 2-spored near gill edge. Cystidia irregularly dispersed (600–800/mm² in most dense areas), (50)60–70 x (6)8–9 µm, slender, subfusiform to clavulate, generally capitulate-appendiculate at tip, originating in subhymenium, thin-walled, with coarsely crystalline contents, reacting strongly and immediately black in sulfovanillin, yellow in KOH. Marginal cells distinct, rendering the gill edge sterile; end cells slender, distinctly or gradually tapering, (15)25–40 x 3–5(6) µm diam, optically empty, occasionally replaced by cheilocystidia. Subhymenium well developed, especially in the gill interspace with more voluminous cells resembling the pseudoparenchymatous structure of the pileipellis. Trama with dispersed oleiferous fragments, abundant sphaerocytes, with distinctly encrusted slender hyphae of variable diameter, especially close to the gill margin. Pileipellis orthochromatic in cresyl blue, two-layered; subpellis a slightly gelified layer of thin, clearly encrusted hyphae, 2–3 µm diam, underlying a strongly developed pseudoparenchymatous suprapellis; the latter with basal cells measuring 15–20(30) µm diam, narrowing to 6–10(15) µm diam for the terminal cell, which is sometimes yellowish-oily in KOH. Pileocystidia mainly situated in the subpellis, some ascending from subpellis in between the cells of the suprapellis, long and slender, cylindrical, often attenuated at the tip, with abundant, coarsely crystalline contents. Stipitipellis less well developed than pileipellis, composed of much smaller elements, measuring 4–5(6) µm diam. Caulocystidia numerous and evident because of the abundant, crystalline contents, 39–70 x 5–7 µm, subfusiform to subcylindrical, minutely capitulate to appendiculate. Clamps absent.

Habitat. – Terrestrial, solitary or scattered, among leaves, in deciduous or mixed broadleaf forests.

Distribution. – Maine:. YORK COUNTY., St Francis Monastery, Kennebunkport, in mixed Pinus-Betula stands, 26 Jan 1987, Fatto 228 (NYBG).

Mississippi:. JACKSON COUNTY, Black Creek, 12 Mar 1988, Fatto 372 (NYBG).

New Jersey:. MONMOUTH COUNTY, Assunpink Wildlife Management Area, 5 Sep 2004, Boyd 04.0905 (priv. herb.).

New York:. ORANGE COUNTY, Rutger’s Creek Wildlife Cons., Greenville, 24 Jul 2003, Boyd 03.0724 (priv. herb.); New York city, in lawn, New York Botanical Garden, 6 Jul 2005, R. Halling 8697 (NYBG)

North Carolina:. BUNCOMBE COUNTY, Asheville, brought in from NAMA excursions from mixed deciduous oak forest, 16 Jul 2004, Buyck 04-282 (PC, holotypus), 17 Jul 2004, Buyck 04-284 (PC), Buyck 04-294 (PC); ORANGE COUNTY, Compartment 71 of Duke Forest S. of railroad tracks, N of power lines, 31 Aug 2000, Rytas Vilgalys 2000/26 (DHN 8518).

Pennsylvania:. FRANKLIN COUNTY, Mont Alto, 8 Aug 2003, Boyd 03.0808 (priv. herb.), ibid., 13 Aug 2005, Buyck 05.104 (PC).

Texas:. NEWTON COUNTY, Bleakwood, along Texas 87, D. Lewis property, mixed broadleaf forest, 8 Jul 2002, Buyck 02-194 (PC), Canyon rim, Mayflower, mixed deciduous with dominance of beech, 29 Jul 2005, Buyck 05.074, 05.085 (PC).

West Virginia:. MONONGALIA COUNTY, Tibbs Run, 29 Jul 2002, Emily Johnson s.n. (DEWV 3712); Panther State Forest, in sandy floodplain with Tsuga canadensis, Carya sp., Quercus sp., Betula sp., MCDOWELL COUNTY, 10 Jul 2002 Donna M. Mitchell DMWV02-297 (DEWV 2862). MONROE COUNTY, Moncove Lake State Park Pinus strobus, Quercus coccinea, Q. rubra, 21 Aug 2003, Donna M. Mitchell DMWV03-1051 (DEWV 4811). BARBOUR COUNTY, on lawn in cemetery between Meadowville and Philippi, under Quercus sp., 22 Aug 2001, William C. Roody WRWV01-852 (DEWV 1800). RALEIGH COUNTY, Steven’s Lake, on ground near Pinus strobus, Quercus alba, Carya sp., Quercus sp., 24 Sep 2003, William C. Roody WRWV03-1329 (DEWV 4885). GILMER COUNTY, Cedar Creek State Park, on ground near Fagus grandifolia, Carya sp., Quercus sp., Liriodendron tulipifera, 6 Aug 2003, William C. Roody WRWV03-638 (DEWV 4414). NICHOLAS COUNTY, Carnifax Ferry State Park, on ground near Tsuga canadensis, Quercus sp., 7 Aug 2003, William C. Roody WRWV03-662 (DEWV4503).

	DISCUSSION

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Microscopic variability is evident in this taxon with regard to spore ornamentation, shape of pileal terminal cells and dermatocystidia. For the latter, variation ranges from few and with poor contents (e.g. Buyck 04-282) to many and with abundant, refractive contents (e.g. Boyd 0724). In some collections the form of the terminal cells in the pileipellis is more frequently ampullaceous to rostrate-appendiculate (e.g. Boyd 0905, DEWV 1800), while in others obtusely convex (e.g. DEWV 4811).

Spores vary considerably in size—not only among collections, but also within a single individual—as well as in ornamentation height and distribution (especially the relative abundance of linear elements versus isolated warts). Some collections have spores with large, almost droplet-like warts. This phenomenon seems to occur when fruiting conditions at the time of spore development are not ideal. Atypical for section Heterophyllae, this new taxon can have spores with an amyloid, suprahilar plage.

As mentioned above it is easy to separate R. parvovirescens under the microscope from other palespored, mild russulas that have a similar appearance in the field (i.e. R. crustosa Peck and R. virescens Fr.). These species have much more slender, less voluminous extremities in the pileipellis ending in more narrow, subulate, terminal cells. Some collections of R. crustosa, however, may have equally short, but in this case much less voluminous, narrower, terminal cells. Because of the much smaller size of these cells in R. crustosa, confusion with this new species is excluded. On the other hand the virescens-crustosa group is much more complex than suspected and embraces at least a dozen taxa in the eastern US as suggested by a forthcoming molecular study (Buyck et al 2005). A provisional identification key to these taxa has been posted at http://www.mtsn.tn.it/russulales-news/id_virescentinae.asp.

Some other Russula species in sect. Heterophyllae Fr., such as R. aeruginea Fr., R. redolens Burl., R. variata Bann., R. heterophylla Fr. or R. subgraminicolor Murrill, also might be confused because of their green pilei. The aforementioned green Russulas, however, have cap surfaces that are never so strongly disrupted or fragmented as in R. parvovirescens.

	ACKNOWLEDGMENTS

 
The senior author thanks Rytas Vilgalys for his support and facilities offered while working at Duke. The authors are grateful to Glenn Boyd and David Lewis for access to their collections and to the curators of NYBG, DEWV, TENN and NYS for the loan of specimens. Ania Boyd is acknowledged for help with county references.

	FOOTNOTES

 
Accepted for publication May 19, 2006.

¹ Corresponding author. E-mail: buyck{at}mnhn.fr

	LITERATURE CITED

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Buyck B. 1989. Utilité taxonomique du bleu de crésyl dans le genre Russula. Persoon. Bull. trimestriel Soc. Mycol. France 95:1–6.

———. 1991. The study of microscopic features in Russula. 2. sterile cells of the hymenium. Russulales News 1: 62–85.

———. 2004. Short diagnoses and descriptions for some exotic Russula (Basidiomycotina). Cryptogamie-Mycologie 25(2):127–128.

———, Mitchell D. 2003. Russula lentiginosa spec nov. from West Viriginia, USA: a probable link between tropical and temperate Russula groups. Cryptogamie-Mycologie 24(4):317–325.

———, Parrent J, Vilgalys R. 2005. The Russula virescenscrustosa species complex (Russulales, Basidiomycotina) from eastern North America. Inoculum 56(4):11.

Kibby G, Fatto RM. 1990. Key to the species of Russula in northeastern North America. 3rd ed., Kibby-Fatto enterprises. 61 p.

Kornerup A, Wanscher JH. 1978. Methuen handbook of colour. 3rd ed. London: Methuen & Co. 252 p.

Romagnesi H. 1967. Russules d’Europe et d’Afrique du Nord. Bordas, Parigi, 998 p.

Woo B. 1989. Trial field key to the species of Russula in the Pacific Northwest. A macroscopic field key to selected common species reported from Washington, Oregon, and Idaho. Ed. Pacific Northwest Key Council.

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