Rhodotus is a genus in the Physalacriaceae family of fungi. It is a monotypic genus and consists of the single mushroom species Rhodotus palmatus, known in the vernacular as the netted Rhodotus, the rosy veincap, or the wrinkled peach. This uncommon species has a circumboreal distribution, and has been collected in eastern North America, northern Africa, Europe, and Asia; declining populations in Europe have led to its appearance in over half of the European fungal Red Lists of threatened species. Typically found growing on the stumps and logs of rotting hardwoods, mature specimens may usually be identified by the pinkish color and the distinctive ridged and veined surface of their rubbery caps; variations in the color and quantity of light received during development lead to variations in the size, shape, and cap color of fruit bodies.
The unique characteristics of R. palmatus have made it difficult for taxonomists to agree on how it should be classified, resulting in an elaborate taxonomical history and an extensive synonymy. First named Agaricus palmatus by Bulliard in 1785, it was reclassified into several different genera before becoming Rhodotus in 1926. The familial placement of the genus Rhodotus within the order Agaricales has also been subject to dispute, and the taxon has been transferred variously to the families Amanitaceae, Entolomataceae, and Tricholomataceae. More recently, molecular phylogenetics analysis has helped determine that Rhodotus is most closely related to genera in the Physalacriaceae.
History and etymology
The type species of genus Rhodotus was originally described as Agaricus palmatus in 1785 by French botanist Jean Bulliard; mycologist Elias Magnus Fries later included it under the same name in his Systema Mycologicum. It was transferred to the then newly described genus Rhodotus in a 1926 publication by French mycologist René Maire. The specific epithet is derived from the Latin palmatus, meaning "shaped like a hand"—possibly a reference to the resemblance of the cap surface to the lines in the palm of a hand. Common names for R. palmatus include the netted Rhodotus, the rosy veincap, and the wrinkled peach.
French botanist Claude Gillet called the species Pleurotus subpalmatus in 1876. A 1986 paper reported that the species Pleurotus pubescens, first described by American mycologist Charles Horton Peck in 1891, was the same as Rhodotus palmatus, making their names synonymous. According to the same publication, another synonym is Lentinula reticeps, described by William Alphonso Murrill in 1915, who thought it to be synonymous with Agaricus reticeps (described by Montagne in 1856), Agaricus reticulatus (Johnson, 1880), Agaricus alveolatus (Cragin, 1885), Pluteus alveolatus (Saccardo, 1887), and Panus meruliiceps (Peck, 1905).
The placement of the genus Rhodotus in the Agaricales order is uncertain, and various authors have offered solutions to the taxonomic conundrum. In 1951, Agaricales specialist Rolf Singer placed Rhodotus in the Amanitaceae because of similarities between the tribes Amaniteae and Rhodoteae, such as spore color and ornamentation (modifications of the spore wall that result in surface irregularities), structure of the hyphae and trama, and chlamydospore production during culture growth.
In 1953, French mycologists Robert Kühner and Henri Romagnesi placed Rhodotus in the Tricholomataceae family—a traditional "wastebasket taxon"—on the basis of spore color. In 1969, Besson argued for the placement of Rhodotus with the Entolomataceae after studying the ultrastructure of the spores. By 1986, Singer had revised the placement of Rhodotus in his latest edition of The Agaricales in Modern Taxonomy, noting that "It has formerly been inserted in the family Amanitaceae but is obviously closer to tribus Pseudohiatuleae of the Tricholomataceae." Tribe Pseudohiatuleae included such genera as Flammulina, Pseudohiatula, Cyptotrama, and Callistodermatium. In 1988, a proposal was made to split the Tricholomataceae family into several new families, including a Rhodotaceae family to contain the problematic genus.
The use of molecular phylogenetics has helped to clarify the proper taxonomic placement of Rhodotus. Studies of the ribosomal DNA sequences from a wide variety of Agaric fungi have corroborated Kühner and Romagnesi's placement of Rhodotus in the Tricholomataceae as then understood. A large scale phylogenetic analysis published in 2005 showed Rhodotus to be in the "core Euagarics clade", a name given to a grouping of gilled mushrooms corresponding largely to the suborder Agaricineae as defined by Singer (1986), but also including taxa that were traditionally classified in the Aphyllophorales (e.g., Clavaria, Typhula, Fistulina, Schizophyllum, etc.) and several orders of Gasteromycetes (e.g., Hymenogastrales, Lycoperdales, Nidulariales). These results corroborated a previous study which showed Rhodotus to be part of a clade containing species such as Cyptotrama asprata, Marasmius trullisatus, Flammulina velutipes, Xerula furfuracea, Gloiocephala menieri, and Armillaria tabescens. The genera containing these latter species have been reassigned to the Physalacriaceae family; as of 2009, both Index Fungorum and MycoBank also list Rhodotus as belonging to the Physalacriaceae.
The fruit body of Rhodotus has a cap, and stem without a ring or volva. The cap initially assumes a convex shape before flattening somewhat with age, and typically reaches widths of 2–6 centimeters (0.8–2.4 in). The edges of the cap are rolled inwards, and the cap surface typically has a conspicuous network of lightly colored ridges or veins that outline deep and narrow grooves or pits—a condition technically termed sulcate or reticulate. Between the ridges, the surface color is somewhat variable; depending on the lighting conditions experienced by the mushroom during its development, it may range from salmon-orange to pink to red. The texture of the cap surface is gelatinous, and the internal flesh is firm but rubbery, and pinkish in color.
The gills have an adnate attachment to the stem, that is, broadly attached to the stem along all or most of the gill width. The gills are thick, packed close to each other, with veins and color similar to, but paler than, the cap. Some of the gills do not extend the full distance from the edge of the cap to the stem. These short gills, called lamellulae, form two to four groups of roughly equal length. The stem is 1.5–3.0 cm (0.6–1.2 in) tall and 0.4–0.6 cm (0.16–0.24 in) thick (usually slightly larger near the base), and may be attached to the underside of the cap in a central or lateral manner. Like the cap color, stem size is also affected by the type of light received during fruit body maturation.
In nature, Rhodotus palmatus is sometimes seen "bleeding" a red- or orange-colored liquid. A similar phenomenon has also been observed when it is grown in laboratory culture on a petri dish: the orange-colored drops that appear on the mat formed by fungal mycelia precede the initial appearance of fruit bodies. The mature fruit body will turn green when exposed to a 10% aqueous solution of Iron(II) sulfate (FeSO4), a common mushroom identification test known as iron salts.
In deposit, the spore color of Rhodotus palmatus has been described most commonly as pink, but also as cream colored. Viewed microscopically, the spores of Rhodotus have a roughly spherical shape, with dimensions of 6–7.2 by 5.6–6.5 µm; the spore surface is marked with numerous wart-like projections (defined as verricose), typically 0.5–0.7 µm long. The spores are non-amyloid—unable to take up iodine stain in the chemical test with Melzer's reagent.
The spore-bearing cells, the basidia, are club-shaped and 4-spored, with dimensions of 33.6–43.2 by 5.6–8 µm. Although this species lacks cells called pleurocystidia (large sterile cells found on the gill face in some mushrooms), it contains abundant cheilocystidia (large sterile cells found on the gill edge) that are 27.2–48 by 4.8–8 µm in size. Clamp connections are present in the hyphae. The outer cellular layer of the cap cuticle is made of bladder-shaped, thick-walled hyphae, each individually supported by a small stalk that extends down into a "gelatinized zone".
Chlamydospores are asexual reproductive units made by some fungi that allow them to exist solely as mycelium, a process which helps them survive over periods unsuitable for growth; Rhodotus was shown experimentally to be capable of producing these structures in 1906. The chlamydospores of Rhodotus are thick-walled cells that develop from single hyphal compartments, and have dimensions of 12–8 by 8–6 µm.
Depending on the source consulted, the edibility of Rhodotus palmatus is typically listed as unknown or inedible. The species has no distinguishable odor, and a "bitter" taste, although one early description referred to the taste as "sweet".
As part of a Spanish research study to evaluate the antimicrobial activity of mushrooms, Rhodotus palmatus was one of 204 species screened against a panel of human clinical pathogens and laboratory control strains. Using a standard laboratory method to determine antimicrobial susceptibility, the mushroom was shown to have moderate antibacterial activity against Bacillus subtilis, and weak antifungal activity against both Saccharomyces cerevisiae and Aspergillus fumigatus.
Habitat and distribution
Rhodotus palmatus is saprobic, meaning it obtains nutrients from decomposing organic matter. It grows scattered or clustered in small groups on rotting hardwoods, such as basswood, maple, and especially elm; in Europe it is known to grow on horse chestnut. The mushroom prefers low-lying logs in areas that are periodically flooded and that receive little sunlight, such as areas shaded by forest canopy. A pioneer species in the fungal colonization of dead wood, it prefers to grow on relatively undecayed substrates. It is often found growing on dark-stained wood, especially the dried-out upper parts of trunks that have lost their bark. R. palmatus tends to fruit in cooler and moister weather, from spring to autumn in the United States, or autumn to winter in Britain and Europe.
Described as having a circumboreal distribution, R. palmatus has been reported from Canada, Iran, Hungary, Italy, Poland, Slovakia, Denmark, Sweden, Norway, Germany, the area formerly known as the USSR, Korea, Japan, and New Zealand. In the United States it has been found in Indiana, and elsewhere in eastern North America. Although often described as "rare", a 1997 study suggests that it may be relatively common in Illinois. It has been suggested that an increase in the number of dead elms, a byproduct of Dutch elm disease, has contributed to its resurgence.
Light at the red end of the visible spectrum has been observed to be required for the development of R. palmatus fruit bodies, contrary to the typical requirement for blue light seen with many other mushroom species. Fruiting occurs in the presence of green, yellow or red light with wavelengths above 500 nm, but only when blue light (under 500 nm) is absent. Consequently, phenotypic variations observed in the field—such as size, shape, and cap color—may be influenced by differing conditions of light color and intensity. For example, specimens grown in the laboratory under green light had fruit bodies with short, straight stems and pale orange, large caps with well-developed ridges and pits, an appearance similar to specimens found in the field that were growing under a canopy of green leaves. Laboratory-grown specimens under amber light had bright orange, small caps with less pronounced reticulations; similarly, field specimens found in autumn, after the leaves had fallen, were more orange to orange-pink in color.
In the 1980s in Europe, increases in the levels of air pollution, as well as changing land use practices coincided with reports of declines in the populations of certain mushrooms. Consequently, a number of fungal conservation initiatives were started to better understand fungal biodiversity; as of October 2007, 31 European countries have produced fungal Red Lists of threatened species. Rhodotus palmatus is a candidate species in over half of the European fungal Red Lists, and is listed as critically endangered, endangered, or near threatened (or the equivalent) in 12 countries. In the Baltic countries Estonia, Latvia, and Lithuania, it is considered by the Environmental Protection Ministries (a branch of government charged with implementing the Convention on Biological Diversity) to be regionally extinct, reported as "extinct or probably extinct". It was one of 35 fungal species to gain legal protection in Hungary in 2005, making it a fineable offense to pick them.
- Bulliard JBF. (1785). Herbier de la France. France. p. plate 216.
- Fries EM. (1821). Systema Mycologicum (in Latin). Lundae: Ex officina Berlingiana. p. 186. Retrieved 2009-09-11.
- Maire R. (1926). "Mycological studies". Bulletin de la Société Mycologique de France (in French) 40 (3): 293–317.
- Findlay WPL. (1967). Wayside and Woodland Fungi. London: F. Warne. p. 130. ISBN 0-7232-0008-4.
- Gaag H van der. (2007). "Rhodotus palmatus: the lonely mushroom" (PDF). McIlvainea 17 (1): 7–8.
- "Fungi of Iowa: Rhodotus palmatus (Bull.: Fr.) Maire". Iowa State University of Science and Technology. Retrieved 2009-06-13.
- McKnight VB, McKnight KH. (1987). A Field Guide to Mushrooms, North America. Boston: Houghton Mifflin Harcourt. p. Plate 19. ISBN 0-395-91090-0.
- Holden, EM (2003). "Recommended English Names for Fungi in the UK: Report to the British Mycological Society, English Nature, Plantlife, and Scottish Natural Heritage" (PDF). Plantlife. Retrieved 2011-12-17.
- Gillet CC. (1874). Les Hyménomycètes ou Description de tous les Champignons (Fungi) Qui Croissent en France. Alençon: CH Thomas. p. 343.
- Peck CH. (1891). "Report of the State Botanist (1890)". Annual Report of the New York State Museum 44: 18. ISSN 1066-9639. OCLC 6435019.
- Redhead SA. (1986). "Mycological observations 15–16: On Omphalia and Pleurotus". Mycologia 78 (4): 522–28. doi:10.2307/3807763. JSTOR 3807763.
- Murrill WA. (1915). "Notes on Agaricus reticeps Mont". Mycologia 7: 290–92.
- Singer R. (1951). "The Agaricales in Modern Taxonomy". Lilloa 22: 1–832.
- Kühner R, Romagnesi H. (1953). Flore analytique des champignons supérieurs (agarics, boletes, chanterelles) (in French). Paris: Masson et Cie. p. 554.
- Besson M. (1969). "Structure de la paroi sporique de Rhodocybe, Rhodotus et Clitopus (Agaricales) [Structure of spore wall of Rhodocybe, Rhodotus and Clitopilus (Agaricales)]". Comptes rendus de l'Académie des sciences, Série D (in French) 269 (2): 142–45.
- Singer 1986, p. 441.
- Singer 1986, pp. 433–35.
- Korf RP. (1988). "Reports (N.S. 1) of the Committee for Fungi and Lichens on Proposals to Conserve and/or Reject Names". Taxon 37 (2): 450–63. doi:10.2307/1222170. JSTOR 1222170.
- Binder M, Hibbett DS, Larsson K-E, Larsson E, Langer E, Langer G. (2005). "The phylogenetic distribution of resupinate forms across the major clades of mushroom-forming fungi (Homobasidiomycetes)". Systematics and Biodiversity 3 (2): 113–57. doi:10.1017/S1477200005001623.
- Moncalvo JM, Vilgalys R, Redhead SA, Johnson JE, James TY, Catherine Aime M, Hofstetter V, Verduin SJ, Larsson E, Baroni TJ, Greg Thorn R, Jacobsson S, Clémençon H, Miller OK. (2002). "One hundred and seventeen clades of euagarics". Molecular Phylogenetics and Evolution 23 (3): 357–400. doi:10.1016/S1055-7903(02)00027-1. PMID 12099793.
- Moncalvo J-M, Lutzoni FM, Rehner SA, Johnson J, Vilgalys R. (2000). "Phylogenetic relationships of agaric fungi based on nuclear large subunit ribosomal DNA sequences". Systematic Biology 49 (2): 278–305. doi:10.1093/sysbio/49.2.278. PMID 12118409.
- "Rhodotus palmatus – Index Fungorum Names record". CAB International. Retrieved 2009-06-12.
- "Rhodotus Maire 1926". MycoBank. Retrieved 2009-09-11.
- Healy RA, Huffman DR, Tiffany LH, Knaphaus G. (2008). Mushrooms and Other Fungi of the Midcontinental United States (Bur Oak Guide). Iowa City: University of Iowa Press. p. 157. ISBN 1-58729-627-6.
- Bas C, Kuyper TW, Noordeloos ME, Vellinga EC, Van Crevel R, Van Os J. (1995). Flora Agaricina Neerlandica—3. CRC. p. 175. ISBN 978-90-5410-616-6.
- Miller OK Jr, Palmer JG, Gillman LS. (1980). "The fruiting and development of Rhodotus palmatus in culture". Mycotaxon 11 (2): 409–19.
- Sundberg WJ, Methven AS, Monoson HL. (1997). "Rhodotus palmatus (Basidiomycetes, Agaricales, Tricholomataceae) in Illinois". Mycotaxon 65: 403–10. Retrieved 2009-09-11.
- Miller HR, Miller OK. (2006). North American Mushrooms: a Field Guide to Edible and Inedible Fungi. Guilford, Conn: Falcon Guide. p. 155. ISBN 0-7627-3109-5.
- Kuo M. "Testing Chemical Reactions". MushroomExpert.Com. Retrieved 2009-09-14.
- Arora D. (1986). Mushrooms Demystified: a Comprehensive Guide to the Fleshy Fungi. Berkeley, California: Ten Speed Press. p. 203. ISBN 0-89815-169-4.
- Jordan M. (1995). The Encyclopedia of Fungi of Britain and Europe. Newton Abbot: David & Charles. p. 175. ISBN 0-7153-0129-2.
- Kuo M. "Rhodotus palmatus". MushroomExpert.com. Retrieved 2009-06-14.
- Pegler DN, Young TWK. (1975). "Basidiospore form in the British species of Clitopilus, Rhodocybe and Rhodotus". Kew Bulletin 30 (1): 19–32. doi:10.2307/4102870. JSTOR 4102870.
- Alexopoulos CJ, Mims CW, Blackwell M. (1996). Introductory Mycology. John Wiley and Sons. pp. 230–31. ISBN 0-471-52229-5.
- Marryat DCE. (1908). "Chlamydospore formation in the Basidiomycete Pleurotus subpalmatus". New Phytologist 7 (1): 17–22. doi:10.1111/j.1469-8137.1908.tb06067.x.
- Phillips R. "Rhodotus palmatus". Rogers Plants Ltd. Retrieved 2009-06-14.
- Suay I, Arenal F, Asensio FJ, Basilio A, Cabello MA, Díez MT, García JB, del Val AG, Gorrochategui J, Hernández P, Peláez F, Vicente MF. (2000). "Screening of basidiomycetes for antimicrobial activities". Antonie van Leeuwenhoek 78 (2): 129–39. doi:10.1023/A:1026552024021. PMID 11204765.
- Rayner ADM, Boddy L. (1988). Fungal Decomposition of Wood: Its Biology and Ecology. John Wiley & Sons Inc. p. 396. ISBN 978-0-471-10310-3.
- Rayner ADM, Hedges MJ. (1982). "Observations of the specificity and ecological role of Basidiomycetes colonizing dead wood". Transactions of the British Mycological Society 78 (2): 370–73. doi:10.1016/S0007-1536(82)80027-2.
- Redhead SA. (1989). "A biogeographical overview of the Canadian mushroom flora". Canadian Journal of Botany 67 (10): 3003–62. doi:10.1139/b89-384.
- Kaminskyj S. "Rhodotus palmatus". University of Saskatchewan. Retrieved 2009-06-14.
- Saber M. (1990). "Contribution to the knowledge of Agaricales pleurotoid in habit in Iran". Iranian Journal of Plant Pathology 26 (1–4): 29–40.
- Siller I. (1999). "Rare macrofungi in the Kekes north forest reserve in the Matra mountains, Hungary". Mikologiai Kozlemenyek (in Hungarian) 38 (1/3): 11–24.
- Migliozzi V, Coccia M. (1998). "Fungi from lazio area. IX. 43–46". Micologia Italiana (in Italian) 27 (3): 25–36.
- Bujakiewicz A, Nita J. (2004). "Żyłkowiec różowawy Rhodotus palmatus (Bull.: Fr.) R. Maire – mieszkaniec białowieskich ostępów". Chrońmy Przyrodę Ojczystą (in Polish) 60 (5): 82–85.
- Ripkova S. (2003). "New, rare and less known macromycetes in Slovakia I". Czech Mycology 55 (3–4): 187–200.
- Vesterholt J. (2005). "Notes on rare fungi collected in Denmark". Svampe 55: 24–38.
- Krieglsteiner GJ. (1979). "1st reports of Ascomycetes and Basidiomycetes in West Germany". Zeitschrift für Mykologie (in German) 45 (1): 35–44.
- Han S-K, Park Y-J, Choi S-K, Lee J-O, Choi J-H, Sung J-M. (2006). "Some unrecorded higher fungi of the Seoraksan and Odaesan National Parks". Mycobiology 34 (2): 56–60. doi:10.4489/MYCO.2006.34.2.056.
- Stevenson G. (1994). New Zealand Fungi: An Illustrated Guide. Christchurch, New Zealand: Canterbury University Press. p. 56. ISBN 978-0-908812-29-5.
- Cooke WB. (1975). "The 1970 Indiana foray". Mycologia 67 (5): 1065–71.
- Dobson FS, Hawksworth DL. (1996). "The Slapton fungal (including lichen) survey: inventorying and documenting changes in the Mycobiota" (PDF). Field Studies 8 (4): 677–84. ISSN 0428-304X. Retrieved 2009-09-22.
- Senn-Irlet B, Heilmann-Clausen J, Genny D, Dahlberg A. (2007). Guidance for Conservation of Macrofungi in Europe (PDF). Strasborg: European Council for the Conservation of Fungi. Retrieved 2009-09-13.
- Dahlberg A. (2007). Excel file European Red List of endangered macrofungi: Red list candidates (Excel file). European Council for the Conservation of Fungi. Retrieved 2009-09-13.
- IUCN East European Programme. (1991). Environmental status reports. Cambridge: International Union for Conservation of Nature and Natural Resources. p. 198. ISBN 2-8317-0161-9.
- Siller I, Dima B, Albert L, Vasas G, Fodor L, Pal-Fam F, Bratek Z, Zagyva I. (2006). "Vedett nagygombafajok Magyarorszagon" [Protected macrofungi in Hungary]. Mikologiai Kozlemenyek (in Hungarian and English) 45 (1/3): 3–158.
- Singer R. (1986). The Agaricales in Modern Taxonomy. 4th rev. ed. Koenigstein: Koeltz Scientific Books. ISBN 3-87429-254-1.
|Wikimedia Commons has media related to Rhodotus palmatus.|