Introduction
Species of Stereocaulon are hosts to a wide range of lichenicolous fungi, with 30 species of fungi belonging to 25 genera having been described on hosts of this genus (Zhurbenko Reference Zhurbenko2010a, Reference Zhurbenkob; Kukwa et al. Reference Kukwa, Etayo and Flakus2012; present publication); these include two genera, viz. Cecidiomyces, described below, and a probable new genus cited as “pyrenomycete 2” in Zhurbenko (Reference Zhurbenko2010a), as well as 19 species that are, as far as is known, confined to Stereocaulon spp.
The diversity of stereocaulicolous fungi in the Holarctic has recently been treated in detail (Zhurbenko Reference Zhurbenko2010a), whereas extra-Holarctic regions are undoubtedly insufficiently explored in this respect. This assumption is supported by the fact that 16 out of 30 species known to occur on Stereocaulon spp. are reported only from the Holarctic, while just three species (Abrothallus stereocaulorum Etayo & Diederich, Plectocarpon stereocaulicola Kukwa et al., and the new Cecidiomyces santessonii) are known exclusively from extra-Holarctic areas (Etayo Reference Etayo2002, Reference Etayo2010; Hafellner & Mayrhofer Reference Hafellner and Mayrhofer2007; Etayo & Sancho Reference Etayo and Sancho2008; Zhurbenko Reference Zhurbenko2010a; Kukwa et al. Reference Kukwa, Etayo and Flakus2012; present publication).
During the course of an examination of the lichenicolous fungi deposited at UPS we found an undescribed gall-inducing hyphomycete on Stereocaulon spp., collected on the subantarctic Macquarie Island (54°30′S, 158°57′E). Attempts to assign this species to any known hyphomycete genus failed. Therefore, a new genus is described to accommodate this fungus.
Material and Methods
The material was examined and photographed using a Zeiss Stemi 2000-CS microscope and Axio Imager A1, equipped with Nomarski differential interference contrast optics. Microscopic examination was carried out on material mounted in water, as well as 10% KOH (K). Conidial dimensions were rounded to the nearest 0·5 µm. The length, breadth and length/breadth ratio (l/b) of conidia are given as: (min.−){
−SD}−{+SD}(−max.), where min. and max. are the extreme values, the arithmetic mean, and SD the corresponding standard deviation. The material examined is housed in the herbaria of the Museum of Evolution, University of Uppsala, Sweden (UPS) and of the V. L. Komarov Botanical Institute in St. Petersburg, Russia (LE).
The New Genus and Species
Cecidiomyces U. Braun & Zhurb. gen. nov.
MycoBank No.: MB 800818
Hyphomycetes. Lichenicolous. Inducing the formation of gall-like swellings on lichen thalli. Mycelium immersed, branched, septate, pigmented. Conidiophores aseptate, reduced to conidiogenous cells, short, little differentiated, semi-macronematous, arising from internal hyphae, erumpent, erect, pigmented, caespitose to sporodochial on the gall surface, holoblastic, monoblastic, determinate, conidiogenous loci terminal, truncate to subtruncate, without any special differentiation. Conidia (‘aleuriosporae’) solitary, subglobose, broadly ellipsoid-ovoid to obovoid or obpyriform, apex broadly rounded, 0–1-euseptate, pigmented, base rounded, truncate to obconically truncate, hila without any special differentiation, conidial secession schizolytic.
Type species: Cecidiomyces santessonii U. Braun & Zhurb.
Etymology. Derived from ‘cecidium’ (kekis, kekidos, Greek origin, gall) and ‘-myces’ (mýkes, Greek origin, fungus).
Cecidiomyces santessonii U. Braun & Zhurb. sp. nov.
MycoBank No.: MB 800819
Lichenicolous gall-inducing hyphomycete forming caespitose to sporodochial colonies on thalli of Stereocaulon species. Conidiophores semi-macronematous, monoblastic, determinate, reduced to conidiogenous cells. Conidia solitary, 0–1-euseptate, pigmented, (12·5–)15·5–20·0(–24)×(9·5)10·5–13·5(–15·0) µm. Conidial secession schizolytic.
Type: Australia, Tasmania, Macquarie Island, E shore of Prion Lake, 54°36′S, 158°55′E, alt. 150 m, on pseudopodetia of Stereocaulon argus growing on rock, 1964, R. Filson 6217 (UPS F-552770—holotype; LE 260898—isotype).
Fig. 1. Cecidiomyces santessonii (UPS F 552775), habitus. Scale=1 mm.
Fig. 2. Cecidiomyces santessonii (holotype). A, portions of colonies; B, conidiophores reduced to conidiogenous cells; C, conidia; D, conidia on conidiogenous cells. Scale=10 µm.
Lichenicolous fungus, inducing the formation of hemispherical, cushion-like to subglobose or somewhat irregularly shaped, basally constricted, often composite gall-like swellings up to 2·5 cm diam., covered by blackish colonies (sometimes with a whitish film probably representing remnants of the host tissues) on pseudopodetia of Stereocaulon species. Mycelium composed of internal hyphae, almost straight to strongly sinuous, branched, septate, at first subhyaline, later brown, thin-walled, smooth to somewhat rough, 1–4 µm wide, loose to dense, forming brown to dark brown stromatic hyphal aggregations. Fructification (colonies) superficial, blackish, loosely to densely caespitose to sporodochial.
Conidiophores aseptate (i.e. reduced to conidiogenous cells), arising from internal hyphae or stromatic hyphal aggregations, erumpent, erect, short, 4–15×3–7 µm, straight to slightly curved-sinuous, unbranched, subcylindrical to somewhat ampulliform or irregular, pale to medium brown, wall slightly thickened, almost smooth to verruculose-rugose, monoblastic, determinate (i.e. with a single, non-proliferating terminal conidiogenous locus), truncate to subtruncate, 2–5 µm broad, without any special differentiation. Conidia formed singly, subglobose, broadly ellipsoid-ovoid to obovoid or obpyriform, apex broadly rounded, base rounded, truncate to obconically truncate, (12·5–)15·5–20·0(–24·0)×(9·5–)10·5–13·5(–15·0) µm, l/b=(1·1–)1·3–1·7(–2·0) (n=62, in water or K), 0–1-septate, septum median or somewhat in the upper or lower half, wall 0·75–2·00 µm thick, smooth or almost so to somewhat rough or irregularly rugose, pigmented, young conidia pale brown, older conidia medium to dark brown, sometimes very dark so that the septum is barely visible, pigmentation uniform or paler below and darker towards the apex, sometimes the upper cell very dark and the lower one much paler, staining umber in K, occasionally with a single or several circular lateral perforations, 0·5–1·5 µm diam., rather inconspicuous in water, but easily visible in K, basal hilum rounded to mostly truncate or almost so, broadly truncate to attenuated, sometimes narrower and peg-like, 3–7 µm wide, wall of the hilum without any special differentiation, conidial secession schizolytic.
Etymology. Dedicated to Rolf Santesson, an outstanding expert in lichenicolous fungi, who selected specimens of the fungus for further studies.
Distribution and hosts. Known from two localities in the subantarctic tundra biome of Macquarie Island. The species grows on healthy-looking saxicolous Stereocaulon species, inducing gall-like swellings on their pseudopodetia.
Additional specimen examined. Australia:Tasmania: Macquarie Island, Mount Waite, 54°39′S, 158°52′E, alt. 375 m, on pseudopodetia of Stereocaulon corticatulum growing on rock, 1964, R. Filson 5956 (UPS F-552775—paratype).
Discussion
A key to lichenicolous hyphomycete genera has recently been published by Diederich in Seifert et al. (Reference Seifert, Morgan-Jones, Gams and Kendrick2011). Attempts to identify the present lichenicolous fungus from the Subantarctic, based on this key, did not lead to any appropriate genus. Due to the simple, little differentiated conidiophores, reduced to monoblastic, determinate conidiogenous cells, giving rise to solitary conidia, this fungus belongs to the Aleuriosporae/Monoblastosporae in the sense of Kiffer & Morelet (Reference Kiffer and Morelet1999). The conidiogenous cells are undoubtedly determinate, i.e. no trace of proliferation has been observed, neither percurrent nor sympodial. The conidial secession is certainly schizolytic. In a few conidia, remnants of conidiogenous cells have been observed which were, however, the result of mechanical treatment during the preparation. In naturally shed conidia such remnants have not been seen. Among other hyphomycete genera hitherto not known to have lichenicolous species, there are only a few with comparable characters. Bactrodesmium Cooke is characterized by having similar conidiophores and conidiogenesis. Its conidia are formed singly, are often unequally pigmented with paler basal cells, and species of this genus may form sporodochial colonies (Ellis Reference Ellis1971, Reference Ellis1976; Kiffer & Morelet Reference Kiffer and Morelet1999; Seifert et al. Reference Seifert, Morgan-Jones, Gams and Kendrick2011), but the conidia are usually phragmosporous with three or more septa, often with dark bands at the septa and, above all, the conidial secession is rhexolytic. Pithomyces Berk. & Broome and Trichocladium Harz are other similar genera (Ellis Reference Ellis1971, Reference Ellis1976; Kiffer & Morelet Reference Kiffer and Morelet1999; Seifert et al. Reference Seifert, Morgan-Jones, Gams and Kendrick2011). However, species of these genera are non-sporodochial hyphomycetes with effuse mycelium and pleurogenous or integrated conidiogenous cells and often only with peg-like lateral conidiogenous denticles. Most species of Pithomyces are phragmo- to dictyosporous, although a few 0–1-septate species have been assigned to this genus, for example P. cupaniae (Syd.) M. B. Ellis and P. africanus M. B. Ellis (Ellis Reference Ellis1971). Pithomyces is easily distinguishable from Cecidiomyces by its rhexolytic conidial secession with conspicuous remnants of conidiogenous cells at the base of the conidia. Trichocladium species are didymo- to scolecosporous (Ellis Reference Ellis1971, Reference Ellis1976) and the conidia may also be unequally pigmented and similar in shape and size. In addition to differences in the structure of the colonies, the conidial secession in Trichocladium is also rhexolytic (Seifert et al. Reference Seifert, Morgan-Jones, Gams and Kendrick2011), although less conspicuous than in Pithomyces. Stanjehughesia Subram. (Subramanian Reference Subramanian1992) is another comparable genus which was segregated from Sporidesmium Link: Fr. based on an absence of conidiophores, that was introduced for former species of the latter genus having conidiophores reduced to conidiogenous cells (McKenzie Reference McKenzie1995; Réblová Reference Réblová1999; Wu & Zhuang Reference Wu and Zhuang2005; Marincowitz et al. Reference Marincowitz, Crous, Groenewald and Wingfield2008; Seifert et al. Reference Seifert, Morgan-Jones, Gams and Kendrick2011). However, Cecidiomyces and Stanjehughesia are only comparable due to their short conidiophores being reduced to conidiogenous cells. All other characters are quite distinct. Stanjehughesia comprises saprobic species occurring on bark, wood, twigs, leaf litter and similar substrata with usually effuse conidiophores, and its conidia are always pluriseptate and more or less scolecosporous. The allocation of the new species to this genus would lead to an inappropriate artificial widening of its circumscription. The position of Stanjehughesia is equivocal. Réblová (Reference Réblová1999) did not recognize this genus and reduced it to synonymy with Sporidesmium. Other authors have accepted Stanjehughesia and added new species (McKenzie Reference McKenzie1995; Wu & Zhuang Reference Wu and Zhuang2005; Marincowitz et al. Reference Marincowitz, Crous, Groenewald and Wingfield2008). Seifert et al. (Reference Seifert, Morgan-Jones, Gams and Kendrick2011) tentatively treated it as a separate genus, keyed out in a special key to genera of the Sporidesmium complex. However, several species assigned to Stanjehughesia are intermediate between this genus and Sporidesmium s. str. in structure of the conidiophores. McKenzie (Reference McKenzie1995) proposed the combination Stanjehughesia decorosa (R. F. Castañeda & W. B. Kendr.) McKenzie (≡Sporidesmium decorosa R. F. Castañeda & W. B. Kendr.) for a species with 0–1-septate, sometimes percurrent conidiophores, and Wu & Zhuang (Reference Wu and Zhuang2005) described S. fasciculata J. Mena et al., characterized by having 0–2-septate and relatively long (30–65×5–7 µm) conidiophores, and S. larvata (Cooke & Ellis) Subram. with 0–2-septate and very short conidiophores. These intermediate species support Réblová's taxonomic concept.
Due to its lichenicolous habit, induction of gall-like swellings on the host thallus, caespitose to sporodochial colonies, semi-macronematous but distinct monoblastic, determinate, aseptate conidiophores (reduced to conidiogenous cells), solitary, 0–1-euseptate conidia, and schizolytic conidial secession, the present subantarctic fungus is assigned to a new hyphomycete genus.
Gall induction, as in Cecidiomyces santessonii, is a common phenomenon in lichenicolous fungi and known in about 80 species (5%) of this ecological fungal group (Grube & de los Ríos Reference Grube and de los Ríos2001). Three other species growing on Stereocaulon, viz. Plectocarpon stereocaulicola, Polycoccum trypethelioides (Th. Fr.) R. Sant., and Rhymbocarpus stereocaulorum (Alstrup & D. Hawksw.) Etayo & Diederich (Zhurbenko Reference Zhurbenko2010a; Kukwa et al. Reference Kukwa, Etayo and Flakus2012), which are all ascoma-forming ascomycetes quite distinct from the new species, also form galls. Other lichenicolous hyphomycetes causing galls, viz. Hawksworthiana peltigericola (D. Hawksw.) U. Braun, Galloea cladoniicola Alstrup & Søchting (possibly not a genuine gall-inducer), Refractohilum galligenum D. Hawksw., R. peltigerae (Keissl.) D. Hawksw., Taeniolella atricerebrina Hafellner, and T. rolfii Diederich & Zhurb. (Hawksworth Reference Hawksworth1977, Reference Hawksworth1980; Braun Reference Braun1995; Diederich & Zhurbenko Reference Diederich and Zhurbenko1997; Hafellner Reference Hafellner2007; Alstrup & Søchting Reference Alstrup and Søchting2009), are also quite distinct and not comparable with the new species.
Cecidiomyces santessonii might easily be added to the worldwide key of fungi growing on Stereocaulon (Zhurbenko Reference Zhurbenko2010a) as a counterpart of Taeniolella christiansenii Alstrup & D. Hawksw., the only other hyphomycete known from this host genus.
We thank Paul Diederich, Rod Seppelt and Vadim Mel'nik for valuable comments on the manuscript.
