Vol. XXI, pp. 241-246 October-December 1984 MERULIUS, A SYNONYM OF PHLEBIA K. K. NAKASONE and H. H. BURDSALL, JR. Center for Forest Mycology Research Forest Products Laboratory 1 USDA, Forest Service Madison, Wis. 53705 ABSTRACT Merulius Fr. is placed in synonymy with Phlebia Fr. Supporting evidence from basidiocarp and culture studies are presented. The new combinations Phlebia tremellosus and Phlebia incarnata are proposed. Keywords: Merulius, Merulius tremellosus, Phlebia, Phlebia radiata INTRODUCTION The similarities and close relationships between Merulius Fr. and Phlebia Fr., as represented by the type species M. tremellosus Schrad.: Fr. and P. radiata Fr., are widely recognized (Parmasto, 1968; Ginns, 1976; Eriksson and Ryvarden, 1976). We, also, have noted the similarities. The genera are maintained separately, but included in the same family--corticiaceae--andthe same subfamily--phlebioideae (Parmasto, 1968, p. 89). Jülich (1982), however, considers Merulius and Phlebia as types of different families. The name Phlebia was proposed by Fries (1821), and he later designated P. radiata Fr. as the type species (1828). When he described the Phlebia, Fries included among the four species P. merismoides Fr., which he had described in 1818 (Table I). This spe cies is often considered to be conspecific with P. radiata and is an earliername. However, P. merismoides has not been used recently, while P. radiata has been generally accepted for the taxon for the past 30 years. To avoid confusion and unnecessary name changes, we prefer to conserve current usage by recognizing P. radiata and place P. merismoides in synonomy. The name Merulius has a longer and more complex history. It was used in the sense of Morchella and of Cantharellus (Donk, 1958) before being validated by Fries (1821) in a different sense. Merulius tremellosus is generally accepted as the lectotype species. Recent concepts of Merulius are more restrictive than Fries's and result in more natural groupings. In fact, current concepts retain only one of Fries's original taxa in Merulius (Table I). 'Maintained in cooperation with the University of Wisconsin.
242 TABLE I Disposition of taxa in Phlebia and Merulius accepted by Fries in 1821. Descriptions of basidiocarps and cultures of the two type species are readily available (Ginns, 1976; Eriksson and Ryvarden, 1976; Eriksson et al., 1981). Because our data agree with the published descriptions, we refer the reader to those accounts. Our intention is to analyze and discuss the significant similarities and differences between the two species. The data here support our conclusion that Phlebia and Merulius are congeneric. GENERAL OBSERVATIONS Basidiocarp observations.--basidiocarps of P. radiata and M. tremellosus are readily distinguishable. Phlebia radiata is entirely effuse although the margins are loosely attached and often can be pulled away from the substrate. The hymenophore is tuberculate and rarely develops either small pits or anastomosing ridges. Merulius tremellosus is effuse-reflexed with a radially arranged, pitted hymenophore. Eriksson and Ryvarden (1976, p. 863) and Jülich (1982, p. 176, 178) maintain the genera are distinct because of the "dimorphic trama" in Merulius. Ginns (1976, pp. 139, 153), however, found this charac ter to be present in both species. We concur with his findings. Several microscopic characters of these species are similar: thickening subhymenium, brownish-orange granular to amorphous mate rial in the hymenium and subhymenium, cystidia, narrowly clavate
243 basidia, andsmooth, cylindricalbasidiospores. However, there are some differences. Ginns (1976, p. 102) reports that the basidia in M. tremellosus arise sympodially while in P. radiata they are cyme- like. Weobserved, however, that the basidia in P. radiataand M. tremellosus are produced from sympodially branched hyphae (also see Figs. 432, 589, and 590 in Corticiaceae of North Europe (Eriksson and Ryvarden, 1976; Eriksson et al., 1981)). In addition the subiculum in P. radiata also develops densely staining, broad hyphae that originate in the margins as cylindrical to clavate hyphal end cells. These hyphal end cells are morphologically similar to the cystidia of the subhymenium and hymenium. They are not found in the subiculum of M. tremellosus. The cystidia in P. radiata never pro trude beyond the hymenium and are larger than those in M. tremellosus, which protrude slightly above the basidia. However, we interpret these differences to be important only at the species level. TABLE II Growth characters of Phlebia radiata and Merulius tremellosus after 1 week incubation on three standard media. TABLE III Summary of some significant microscopic cultural characters of P. radiata and M.tramellosus.
244 Cultural and other observations.--whereas P. radiata grows rapidly on malt extract agar, the growth rate of M. tremellosus is variable. Both species react strongly and grow substantially on gallic acid and tannic acid agars (Table II). The advancing zone hyphae in both spe cies are simple-septate, but later clamp connections develop on all otherhyphae. This combination of characters places these species in a unique group of fungi, Group 54 of Nobles (1958). This group of fungi includes most true Phlebia species, as well as Mycoacia fuscoatra (Fr.: Fr.) Donk, Hyphodontia setulosa (Berk. et Curt.) Maas G., Poria cinerascens (Bres.) Sacc. et Syd., Poria rivulosa (Berk. et Curt.) Cke., and Poria subvermispora Pilát. Although P. radiata and M. tremellosus can be easily differen tiated microscopically in culture (Table III), we contend that the presence or absence of cystidia or asexual spores are important only at the species level. Additionally, both species are associated with a white-rot decay of logs and slash and possess a bipolar incompati bility system (Boidin, 1956; Ginns, 1976; and our results). Specimens examined: As Phlebia radiata: Sweden-+mole: Femsjö, E. Fries, 2 specimens; Femsjö [på bark av Fagus sylvatica], herb. E. Fries, 2 specimens, (one is designated NEOTYPE, here selected, of Phlebia radiata) ~- (University of Uppsala--UPS). As Merulius tremellosus: Sweden--Uppsala,Halmbyboda, E. P. Fries, 1853; Lundell 5650, on Betula, Småland, Femsjö; Fungi Suecici, Lundell 4100, on Fagus; Femsjö, Fung. exsic. Suecici 249, frondose trees, Hofgärden (UPS). CONCLUSIONS Phlebia and Merulius traditionally have been maintained as dis tinct primarily because of the basidiocarp habit and the configuration of the hymenophore. We contend that these characters are not suffi ciently important to delimit taxa at the generic level. Phlebia and Merulius are so similar morphologically and biologically that recog nizing them as distinct genera is unwarranted. The cultural and basidiocarp differences observed are important only at the species level. Because we consider Merulius and Phlebia congeneric, one of the names must be chosen to represent the genus. Either name could be chosen because both were published by Fries (1821) in the same work, and page priority is not recognized by the International Code of Botanical Nomenclature (Voss et al., 1983). The decision was straightforward for us, considering the following facts: 1) If Merulius is placed in synonymy with Phlebia, only two new combinations will be required. 2) If Phlebia is placed in synonymy under Merulius, nearly 50 new combinations will be required. 3) There is good mate rial of P. radiata to serve as neotype. Thus, we propose to recognize Phlebia and place Merulius in synonymy. Phlebia Fr. emend.: Fruitbody effuse to effuse-reflex or dimidiate, cartilaginous, subgelatinous or ceraceous; hymenophore smooth to hydnaceous or merulioid; hyphal system monomitic; subiculum compact to tightly agglutinated, sometimes dimorphic with loosely interwoven hyphae near substrate, reflexed abhymenial layer also of loosely interwoven hyphae; subicular hyphae hyaline, thin- to thick- walled, usually nodose septate, with or without a gelatinous matrix;
245 subhymenium thickening; cystidia absent or present, then smooth or encrusted; basidia narrowly clavate, in a dense palisade; basidio spores hyaline, smooth, thin-walled, ellipsoid to allantoid, nonamyloid, acyanophilous. Neotype: Phlebia radiata på bark av Fagussylvatica, Femsjö (herb. E. Fries, UPS). The following new combinations are required: Phlebia tremellosus (Schrad.: Fr.) Nakas. et Burds., comb. nov. (Basionym--Merulius tremellosus Schrad.: Fr., Syst. Mycol. 1:327. 1821) and Phlebia incarnata (Schw.) Nakas. et Burds., comb. nov. (Basionym--Merulius incarnatus Schw., Nat. Ges. Leipzig Schr. 1:92. 1822). The choice of a neotype specimen to represent P. radiata was dif ficult. Four specimens of P. radiata were available from the Fries herbarium, but none agreed entirely with data from the original description. All were collected in Femsjö and labeled in Fries's handwriting, but only two labels indicated that he was the collector. None of the specimens had a substrate stated on the original label, although two specimens were annotated later by Fries as occuring on Fagus sylvatica. We have chosen one of the specimens on Fagus sylvatica (annotated "Designated Neotype, HHB & KKN") as the neotype, for the following reasons: 1) The neotype is on Fagus which differs from Fries's original diagnosis, which states it occurs on Betula. Later, however, in the Elenchus Fungorum (Fries, 1828), he indicated P. radiata occurs on Fagus also. Phlebia radiata occurs on many genera of hardwood trees, so the substrate is not critical to the species concept. 2) The morphological characters of the neotype specimen agree with the original description and the neotype specimen is in good condition. The other three specimens cited (in Specimens Examined) appear to be portions of the same collec tion as the neotype. 3) Fries had actually seen and identified this specimen. 4) The current species concept will be maintained. Merulius tremellosus also lacks a type specimen. Thus, we searched for an appropriate specimen to serve as neotype. None of the specimens obtained from UPS were available to Fries when he described the species. Only one specimen (collected by E. P. Fries in 1853) could have been considered by Fries to be included in any of his pub lications. Unfortunately, it is inadequate to serve as a neotype. Therefore, we here designate the specimen labeled "Fungi Suecici 4100, Merulius tremellosus Schrad. ex Fr., på murken bokstubbe, Sm. Femsjö sn, Hägnen 21.IX. 1940. leg. Seth Lundell" (UPS) as the neotype of Merulius tremellosus Schrad.: Fr. This specimen is of adequate size and is in excellent condition. It was collected in Femsjö where Fries commonly collected, so is probably the concept he recognized. It agrees with the currently accepted concept of the species. ACKNOWLEDGMENTS The herbarium of University of Uppsala lent specimens used in this study. Dr. Michael J. Larsen, Dr. James H. Ginns, and MS. Frances F. Lombard reviewed this manuscript and provided helpful comments.
246 LITERATURE CITED