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A phylogenetic re-evaluation of Arthrinium

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Abstract

Although the genus Arthrinium (sexual morph Apiospora) is commonly isolated as an endophyte from a range of substrates, and is extremely interesting for the pharmaceutical industry, its molecular phylogeny has never been resolved. Based on morphology and DNA sequence data of the large subunit nuclear ribosomal RNA gene (LSU, 28S) and the internal transcribed spacers (ITS) and 5.8S rRNA gene of the nrDNA operon, the genus Arthrinium is shown to belong to Apiosporaceae in Xylariales. Arthrinium is morphologically and phylogenetically circumscribed, and the sexual genus Apiospora treated as synonym on the basis that Arthinium is older, more commonly encountered, and more frequently used in literature. An epitype is designated for Arthrinium pterospermum, and several well-known species are redefined based on their morphology and sequence data of the translation elongation factor 1-alpha (TEF), beta-tubulin (TUB) and internal transcribed spacer (ITS1, 5.8S, ITS2) gene regions. Newly described are A. hydei on Bambusa tuldoides from Hong Kong, A. kogelbergense on dead culms of Restionaceae from South Africa, A. malaysianum on Macaranga hullettii from Malaysia, A. ovatum on Arundinaria hindsii from Hong Kong, A. phragmites on Phragmites australis from Italy, A. pseudospegazzinii on Macaranga hullettii from Malaysia, A. pseudosinense on bamboo from The Netherlands, and A. xenocordella from soil in Zimbabwe. Furthermore, the genera Pteroconium and Cordelia are also reduced to synonymy, rejecting spore shape and the presence of setae as characters of generic significance separating them from Arthrinium.

Introduction

The genus Arthrinium (sexual morph Apiospora; Ellis 1971, Seifert et al. 2011) is widespread and ecologically diverse. It commonly occurs as a saprobe on grasses, and also on leaves, stems and roots of a range of different plant substrates (Agut & Calvo 2004). Arthrinium is ecologically diverse, and has been reported as a plant pathogen, with A. arundinis causing kernel blight of barley (Martínez-Cano et al. 1992), and A. sacchari causing damping-off of wheat (Mavragani et al. 2007). It is reported as an endophyte in plant tissue (Ramos et al. 2010), lichens (He & Zhang 2012), and marine algae (Suryanarayanan 2012). Arthrinium phaeospermum causes cutaneous infections of humans (Rai 1989, Zhao et al. 1990, de Hoog et al. 2000).

Isolates of Arthrinium produce a range of interesting extrolites in culture, some of which exhibit significant toxicity against human cancer cell lines (Klemke et al. 2003), or inhibit a broad range of human pathogenic filamentous fungi, yeasts, and bacteria (Cabello et al. 2001, Ramos et al. 2010). An endophytic isolate of A. phaeospermum produces growth-promoting substances in Carex kobomugi, a plant surviving under extreme conditions on sand dunes in Korea (Khan et al. 2009).

The genus Arthrinium was described in 1817 and has numerous generic synonyms (Seifert et al. 2011). One such generic name with uncertain status is Pteroconium, introduced in 1892, which Ellis (1971, 1976) and Seifert et al. (2011) retained as separate from Arthrinium, in spite of its Apiospora sexual morph. Cordella is another potential synonym of Arthrinium, distinguished chiefiy by possessing setae. During this study several interesting isolates were collected, including ones of P. pterospermum, the type species of Pteroconium. The decision to move to a single nomenclature is explained elsewhere (Hawksworth et al. 2011, Wingfield et al. 2012), and adopted here in accordance with the current Code. Although both genera (Arthrinium and Apiospora) have a similar number of species, Arthrinium is older and more commonly encountered and referred to in the literature than Apiospora introduced in 1875. Following the principles advocated by Hawksworth (2012) for dealing with names in the present period of transition, we propose that in future Arthrinium be used when referring to these taxa. No in-depth phylogenetic analysis has thus far been published on Arthrinium, which is placed in Apiosporaceae (Sordariomycetes) (Hyde et al. 1998, Lumbsch & Huhndorf 2010). The aims of the present study were to resolve the potential synonymy of Arthrinium, Cordella, and Pteroconium, elucidate the higher classification and phylogeny of Apiosporaceae, and at the same time provide a more robust tree for species of Arthrinium.

Materials and Methods

Isolates

Fresh collections were made from debris of diverse hosts by placing material in damp chambers for 1–2 d. Single conidial colonies were established from sporulating conidiomata on Petri dishes containing 2 % malt extract agar (MEA; Crous et al. 1991, 2009b). Additional strains were obtained from the culture collection of the CBS-KNAW Fungal Biodiversity Centre (CBS) Utrecht, The Netherlands. Colonies were subcultured onto potato-dextrose agar (PDA), oatmeal agar (OA), MEA (Crous et al. 2009b), and pine needle agar (PNA) (Smith et al. 1996), and incubated at 25 °C under continuous near-ultraviolet light to promote sporulation. Reference strains are deposited in CBS.

DNA isolation, amplification and analyses

Genomic DNA was extracted from fungal colonies growing on MEA using the UltraClean™ Microbial DNA Isolation Kit (MoBio Laboratories, Solana Beach, CA, USA) according to the manufacturer’s protocol. The primers V9G (de Hoog & Gerrits van den Ende 1998) and LR5 (Vilgalys & Hester 1990) were used to amplify the nuclear rDNA operon spanning the 3’ end of the 18S rRNA gene, the first internal transcribed spacer (ITS1), the 5.8S rRNA gene, the second ITS region and the 5’ end of the 28S rRNA gene. The primers ITS4 (White et al. 1990) and LSU1Fd (Crous et al. 2009a) were used as internal sequence primers to ensure good quality sequences over the entire length of the amplicon. Part of the translation elongation factor 1-alpha (TEF) was amplified and sequenced using primers EF1-728F (Carbone & Kohn 1999) and EF-2 (O’Donnell et al. 1998), while T1 (O’Donnell & Cigelnik 1997) and Bt-2b (Glass & Donaldson 1995) were used for the beta-tubulin gene region (TUB). Amplification conditions for ITS, LSU and TEF followed Crous et al. (2013) and for TUB, Lee et al. (2004). Megablast searches (Altschul et al. 1997) using the ITS and LSU sequences were performed in NCBI’s GenBank nucleotide sequence database to identify the closest matching sequences, which were added to the sequence alignment. The sequence alignment and subsequent phylogenetic analyses for all the above were carried out using the methods in Crous et al. (2006). Gaps longer than 10 bases were coded as single events for the phylogenetic analyses (only for ITS and TEF; see alignment in TreeBASE: ID 14349); the remaining gaps were treated as “fifth state” data in the parsimony analyses. For the LSU alignment, MrModeltest v. 2.2 (Nylander 2004) was used to determine the best nucleotide substitution model settings prior to the Bayesian analysis in MrBayes v. 3.2.1 (Ronquist et al. 2012). Sequences derived in this study were lodged at GenBank, the alignments and trees in TreeBASE (https://doi.org/www.treebase.org/treebase/index.html), and taxonomic novelties in MycoBank (https://doi.org/www.MycoBank.org; Crous et al. 2004).

Morphology

Observations were made with a Zeiss V20 Discovery stereo-microscope, and with a Zeiss Axio Imager 2 light microscope using differential interference contrast (DIC) illumination and an AAxioCam MRc5 camera and software. Measurements and photographs were made from structures mounted in clear lactic acid. The 95 % confidence intervals were derived from 30 observations (× 1000 magnification), with the extremes given in parentheses. Ranges of the dimensions of other characters are given. Colony characters and pigment production were noted after 2 wk of growth on MEA, PDA and OA (Crous et al. 2009b) incubated at 25 °C. Colony colours (surface and reverse) were rated according to the colour charts of Rayner (1970). Morphological descriptions were based on cultures sporulating on PDA.

Results

Phylogeny

Amplicons of approximately 1700 bases were obtained of the partial 18S rRNA, full length ITS and partial 28S rRNA (LSU) genes for the isolates in Table 1, and approximately 750 bp and 450 bp for TUB and TEF, respectively. The LSU alignment was used to resolve the generic placement of strains (Fig. 1) and the ITS to determine species identification (Fig. 2; discussed in species notes where applicable). The combined TEF and TUB alignment (Fig. 3) was used to confirm the species resolution of ITS and that no cryptic species complexes were present. As each alignment addressed a specific research question (LSU: genera, ITS: species as the standard barcode region, and TEF and TUB to resolve species complexes, if any), a combined tree based on all four loci was not generated. In addition, such a combined tree would be based on an alignment which includes some missing sequences and would, therefore, not be as robust as the phylogenetic trees presented in Figs 13.

Table 1 Details of strains included in the phylogenetic analyses.
Fig. 1
figure1

Consensus phylogram (50 % majority rule) of 3 984 trees resulting from a Bayesian analysis of the LSU sequence alignment using MrBayes v. 3.2.1. Bayesian posterior probabilities are indicated at the nodes and the scale bar represents the expected changes per site. Families are indicated in coloured blocks and species names in black text. GenBank accession numbers for downloaded sequences are shown after species names and culture collection numbers before species names. The tree was rooted to Hypocrea gelatinosa (GenBank JN941453).

Fig. 2
figure2

The first of 72 equally most parsimonious trees obtained from an analysis of the ITS sequence alignment (TL = 552 steps, CI = 0.621, Rl = 0.938, RC = 0.583). The numbers at the nodes represent bootstrap support values based on 1000 resamplings and thickened lines indicate those branches present in the strict consensus tree. Type and ex-type strains are indicated in bold and the scale bar indicates 30 changes. The culture collection or GenBank accession number is indicated for each sequence, followed by the isolation source and country of origin. The tree is rooted to Seiridium phylicae (GenBank accession KC005787).

Fig. 3
figure3

The first of four equally most parsimonious trees obtained from an analysis of the combined TUB and TEF sequence alignment (TL = 2003 steps, CI = 0.703, RI = 0.875, RC = 0.616). The numbers at the nodes represent bootstrap support values based on 1 000 resamplings and thickened lines indicate those branches present in the strict consensus tree. The scale bar indicates 30 changes. The culture collection number is indicated for each sequence, followed by the isolation source and country of origin. The tree is rooted to Seiridium phylicae (strain CPC 19965; GenBank accessions KC005821 and KC005817 for TUB and TEF, respectively).

The manually adjusted LSU alignment contained 80 sequences (including the outgroup sequence), and 791 characters including alignment gaps (available in TreeBASE) were used in the phylogenetic analysis; the data partition contained 199 unique site patterns. Based on the results of MrModeltest, the following priors were set in MrBayes: dirichlet base frequencies and the GTR+I+G model with inverse gamma-distributed. The Bayesian analysis lasted 2 655 000 generations and the 50 % consensus trees and posterior probabilities were calculated from the 3984 trees left after discarding 1328 trees (the first 25 % of generations) for burn-in (Fig. 1). All Apiospora and Arthrinium strains clustered in a well-supported clade indicated in Fig. 1 as the family Apiosporaceae.

The manually adjusted ITS alignment contained 72 sequences (including the outgroup sequence), and 514 characters including alignment gaps (available in TreeBASE) were used in the phylogenetic analysis. Of these characters, 157 were parsimony-informative, 51 variable and parsimony-uninformative, and 306 constant. The parsimony analysis of the ITS alignment yielded 72 equally most parsimonious trees (TL = 552 steps; CI = 0.621; RI = 0.938; RC = 0.583). Some species, e.g. A. marii and A. sacchari, are not well-supported in the ITS phylogeny (Fig. 2), but well-supported in the combined TUB and TEF phylogeny (Fig. 3).

The manually adjusted combined TUB and TEF alignment contained 39 sequences (including the outgroup sequence) and 1288 characters including alignment gaps (available in TreeBASE) were used in the phylogenetic analysis; 565 of these were parsimony-informative, 51 were variable and parsimony-uninformative, and 486 were constant. The parsimony analysis of the ITS alignment yielded four equally most parsimonious trees (TL = 2003 steps; CI = 0.703; RI = 0.875; RC = 0.616). All included species were well-supported in the combined TUB and TEF phylogeny (Fig. 3).

Taxonomy

The species treated below are those that were available in culture. Several other names exist, but these await to be recollected and subjected to DNA analysis.

Apiosporaceae K. D. Hyde et al., Sydowia 50: 23 (1998).

Description: Conidiophores frequently arising from hyphae or aggregated in a brown stroma, forming black sporodochia, brown to dark brown, forming conidia laterally and terminally. Setae present or absent, brown, smooth, erect, sparsely septate, intermingled among conidiophores. Conidiogenous cells discrete, doliiform to ampulliform to subcylindrical, subhyaline to pale brown, smooth to finely verruculose, aggregated on aerial hyphae, giving rise to clusters of conidia; at times reduced to lateral pegs on hyphae, proliferating sympodially or percurrently. Conidia aseptate, brown to dark brown, smooth to verruculose, guttulate to granular, frequently with equatorial slit of lighter pigment. Stromata immersed in epidermis, becoming erumpent through a longitudinal split, revealing rows of densely arranged perithecial ascomata. Paraphyses broadly filiform, septate, deliquescing early. Ascomata globose with papillate ostioles; wall composed of multiple layers of pseudoparenchymatous cells. Asci 8-spored, unitunicate, clavate to broadly cylindrical. Ascospores bi- to tri-seriate, ellipsoidal, inequilateral, tapered at both ends, apiosporous, 1-septate near the lower end, smooth, hyaline, with or without mucoid sheath.

Type genus: Apiospora Sacc. 1875 (syn. Arthrinium Kunze 1817).

Note: Based on morphology, Hyde et al. (1998) regarded Dictyoarthrinium, Endocalyx, Scyphospora and Spegazzinia as possible members of this family, though this remains to be confirmed, pending molecular studies.

Arthrinium Kunze, in Kunze & Schmidt, Mykol. Hefte 1: 9 (1817) : Fr., Syst. Mycol. 1: xliv (1821).

Type species: A. caricicola Kunze & J.C. Schmidt 1817

Synonyms: Apiospora Sacc., Atti Soc. Veneto-Trent. Sci. Nat., Padova 4: 85 (1875).

Type species: A. montagnei Sacc. 1875

Cordella Speg., Anales Soc. Ci. Argent. 22: 210 (1886).

Type species: C. coniosporioides Speg. 1886 Pteroconium Sacc., Syll. Fung. 10: 570 (1892).

Type species: P. pterospermum (Cooke & Massee) Grove 1914

Additional synonyms are listed in Ellis (1965) and Seifert et al. (2011).

Description: Colonies compact, black to dark brown, superficial to erumpent. Mycelium immersed and superficial. Conidiophores arising from basal cells that are subcylindrical, subhyaline with refractive, thick transverse septa, brown to dark brown, forming conidia laterally and terminally; conidiophores frequently aggregated in a brown stroma, forming black sporodochia on the host and in culture. Setae present or absent, brown, smooth, erect, sparsely septate, tapering to subcute apex, intermingled among conidiophores. Conidiogenous cells discrete, doliiform to ampulliform to subcylindrical, subhyaline to pale brown, smooth to finely verruculose, aggregated on aerial hyphae, giving rise to clusters of conidia; at times reduced to lateral pegs on hyphae, holoblastic, proliferating sympodially (at times clearly phialidic with periclinal thickening, rarely with percurrent proliferation). Conidia aseptate, brown to dark brown, smooth to verruculose, guttulate to granular, with distinctive shape (round, curved, curved with two horns, oblong, irregular, limoniform, fusiform, navicular, dentate or lobed), at times fiattened, with equatorial slit of lighter pigment. Sterile cells when formed replace conidia, usually smaller and paler than conidia, with different shape, frequently containing refractive cubical bodies. Stromata immersed in epidermis, becoming erumpent through a longitudinal split, revealing rows of densely arranged perithecial ascomata. Ascomata globose with papillate ostioles; wall composed of 6–9 layers of pseudoparenchymatous cells. Paraphyses broadly filiform, septate, deliquescing early. Asci 8-spored, unitunicate (appearing bitunicate when young), clavate to broadly cylindrical. Ascospores smooth, hyaline, bi- to tri-seriate, ellipsoidal, inequilateral, tapered at both ends, apiosporous, 1-septate near the lower end, with the lower, smaller cell subglobose; ascospores with our without mucoid sheath.

Notes: The conidiogenesis of Arthrinium species is of particular interest. Conidiogenous cells are generally aggregated on a pale brown stroma, forming sporodochia. They tend to be doliiform to subcylindrical, pale brown, with clear periclinal thickening, as illustrated in Ellis (1965). Given moist conditions, they develop further and become ampulliform, with a promonent, elongated neck. The neck can give rise to conidia either sympodially (appearing as holoblastic loci), or in some cases percurrently, with annelations aggregated at the apex. This variation in conidiogenesis makes it difficult to compare these characters among taxa, as conidiophores can either be hyphae with lateral loci, or be reduced to doliiform conidiogenous cells that can be seen to develop further (or not), and are frequently aggregated in sporodochia. Conidia themselves, however, do not appear to differ between those observed in aerial mycelial strands (conidiophores sensu Ellis 1965) or conidiogenous cells situated on a stroma in a black sporodochium.

Arthrinium arundinis (Corda) Dyko & B. Sutton, Mycotaxon 8: 119 (1979).

Basionym: Gymnosporium arundinis Corda, Icon. fung. 2: 1 (1838).

Synonym: Apiospora montagnei Sacc., N. Giorn. bot. Ital. 7: 306 (1875).

(Fig. 4)

Fig. 4
figure4

Arthrinium arundinis (CBS 133509). A. Colony on PDA. B–F. Conidiogenous cells giving rise to conidia. G. Globose conidia. Bars = 10 µm; B = C, D = E, F.

For further synonyms see Ellis (1965).

Description: Mycelium consisting of smooth, hyaline, branched, septate, 2–3 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, pale brown, smooth, ampulliform, 6–12 × 3–4 µm, apical neck 3–5 µm long, basal part 4–6 µm long. Conidia brown, smooth, globose in surface view, (5–)6–7 µm, lenticular in side view, 3–4 µm diam, with pale equatorial slit.

Culture characteristics: Colonies fiat, spreading, with moderate aerial mycelium. On PDA, MEA and OA surface iron-grey with patches of dirty white, reverse iron-grey.

Specimens examined: Canada: British Columbia: Vancouver, University of British Columbia campus, culm of cultivated Sasa, 13 July 1988, R. J. Bandoni (CBS 449.92); loc. cit., stem of cultivated bamboo, 7 May 1992, R. J. & A. A. Bandoni (CBS 450.92). — Germany: Bromberg, 1912, E. Schaffnit (CBS 106.12). — India: dung, Dec. 1971, B.C. Lodha (CBS 732.71). — Iran: Shabestar, leaf of Hordeum vulgare, B. Askari (CBS 114316). — The Netherlands: Flevoland: Harderbos, dead culms of Phragmites australis, 15 May 1983, W. Gams (CBS 464.83). — Switzerland: Basel, living leaves of Fagus sylvatica, 8 Jan. 2008, M. Unterseher (CBS 124788). — USA: Illinois: Kilbourne, Aspergillus flavus sclerotium buried in sandy field (NRRL 25634 = CBS 133509; isolate submitted for whole genome sequence analysis; https://doi.org/genome.jgi-psf.org/pages/search-for-genes.jsf?organism=Apimo1).

Notes: The present cultures closely fit the original description and concept of Arthrinium arundinis, inclusive of the sexual morph, which is a commonly occurring, widely distributed species. Although this present taxon needs to be epitypified, we refrain for doing it here, as we have not yet traced the holotype specimen.

Arthrinium aureum Calvo & Guarro, Trans. Br. mycol. Soc. 75: 156 (1980)

(Fig. 5)

Fig. 5
figure5

Arthrinium aureum (CBS 244.83). A. Colony on MEA. B–G. Conidiogenous cells giving rise to conidia. H. Conidia. Scale bars = 10 µm; B = C–G.

Type: Spain: Barcelona, from air, 1977, A. Calvo & J. Guarro (CBS 244.83 — ex-type culture).

Description: Calvo & Guarro (1980).

Arthrinium hydei Crous, sp. nov.

MycoBank MB804339

(Fig. 6)

Fig. 6
figure6

Arthrinium hydei (CBS 114990). A. Colony on OA. B–E. Conidiogenous cells giving rise to conidia. F. Globose conidia in surface view. G. Lenticular in side view, with pale equatorial slit. Bars = 10 µm; B = C, E = F.

Etymology: Named in honour of Kevin D. Hyde, who collected this fungus in Hong Kong, and has published extensively on the genus.

Diagnosis: Conidia brown, finely roughened, globose in surface view, lenticular in side view, (15–)17–19(–22) µm diam in surface view, (10–)11–12(–14) µm diam in side view.

Type: Hong Kong: New Territories: Tai Po Kau, on culms of Bambusa tuldoides, 19 Apr. 1999, K. D. Hyde (CBS H-21272 — holotype; CBS 114990 — ex-type culture).

Description: Mycelium consisting of smooth, hyaline to pale brown, branched, septate, 2–3 µm diam hyphae. Conidiophores pale brown, smooth, subcylindrical, transversely septate, branched, 20–40 × 3–5 µm. Conidiogenous cells aggregated in clusters on hyphae, brown, smooth, subcylindrical to doliiform to lageniform, 5–8 × 4–5 µm. Conidia brown, roughened, globose in surface view, lenticular in side view, with pale equatorial slit, (15–)17–19(–22) µm diam in surface view, (10–)11–12(–14) µm diam in side view, with a central scar, 1.5–2 µm diam.

Culture characteristics: Colonies fiat, spreading, with sparse aerial mycelium. On PDA surface and reverse pale luteous. On OA surface dirty white with patches of olivaceous-grey, reverse pale luteous. On MEA surface and reverse pale luteous.

Notes: Originally identified as Apiospora sinensis, a species described from a dead petiole of Trachycarpus fortune collected in China (Hyde et al. 1998), but the conidia of A. hydei are much larger than that reported for A. sinensis, 9–12 × 6–8 µm; those of the latter species fall in the range of A. phaeospermum.

Arthrinium kogelbergense Crous, sp. nov.

MycoBank MB804340

(Fig. 7)

Fig. 7
figure7

Arthrinium kogelbergense (CBS 113333). A–C. Conidiogenous cells giving rise to conidia. D. Globose to ellipsoid conidia. Bars = 10 µm.

Etymology: Named after the Kogelberg Nature Reserve, where the ex-type strain of this fungus was collected.

Diagnosis: Conidia brown, smooth, finely guttulate, globose to ellipsoid in surface view, lenticular in side view, (8–)9–10 × 7–8(–9) µm in surface view, 4–5 µm diam in side view.

Type: South Africa: Western Cape Province: Kogelberg Nature Reserve, dead culms of Restionaceae, 11 May 2001, S. Lee (CBS H-21271 — holotype; CBS 113333 — ex-type culture).

Description: Mycelium consisting of smooth, hyaline, branched, septate, 3–5 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, pale brown, smooth, doliiform to subcylindrical, 5–12 × 4–5 µm. Conidia brown, smooth, finely guttulate, globose to ellipsoid in surface view, lenticular in side view, with pale equatorial slit, (8–)9–10 × 7–8(–9) µm in surface view, 4–5 µm diam in side view, with central scar, 1.5–2 µm diam.

Culture characteristics: Colonies flat, spreading, with moderate aerial mycelium. On PDA, MEA and OA surface dirty white, reverse pale luteous to sienna.

Additional specimens examined: Croatia: Adriatic Coast, unknown alga, E. Eguereva (CBS 117206). – South Africa: Western Cape Province: Jonkershoek Nature Reserve, dead culms of Cannomois virgata, 15 July 2001, S. Lee (CBS 113332; Helderberg Nature Reserve, dead culms of Restio quadratus, 13 Apr. 2002, S. Lee (CBS 113335). — Sweden: Uppland: Börstil par., on Juncus gerardi, 2 Aug. 1990, K. & L. Holm (CBS 114734 = UPSC 3251).

Notes: Arthrinium kogelbergense is morphologically close to A. phaeospermum, which has conidia that are slightly longer, (9–)10(–12) µm diam in surface view, and wider, 6–7 µm diam in side view.

Arthrinium malaysianum Crous, sp. nov.

MycoBank MB804342

(Fig. 8)

Fig. 8
figure8

Arthrinium malaysianum (CBS 102053). A. Colony on OA. B–E. Conidiogenous cells giving rise to conidia. F. Globose conidia in surface view. Bars = 10 µm.

Etymology: Named after the country where one of the strains was collected, Malaysia.

Diagnosis: Conidia brown, smooth, globose in surface view, lenticular in side view, 5–6 diam in surface view, 3–4 µm diam in side view.

Type: Malaysia: Gombak, on Macaranga hullettii stem colonised by ants, Aug. 1999, W. Federle (CBS H-21269 — holotype; CBS 102053 — ex-type culture).

Description: Mycelium consisting of smooth, hyaline, branched, septate, 2–3 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, hyaline to pale brown, smooth, doliiform to clavate to ampulliform, 4–7 × 3–5 µm. Conidia brown, smooth, globose in surface view, lenticular in side view, with pale equatorial slit, 5–6 µm diam in surface view, 3–4 µm diam in side view.

Culture characteristics: Colonies fiat, spreading, with fiuffy aerial mycelium. On PDA surface dirty white, with patches of iron-grey due to sporulation, reverse luteous to sienna.

Additional specimen examined: Unknown country: stem base of Cinnamomum camphora, CBS 251.29.

Notes: Conidial dimensions are close to, but slightly longer than those of Arthrinium euphorbiae, (4–)4.7(–5.5) µm in surface view, (3–)3.2(–4) µm in side view (from Euphorbia, collected in Zambia; Ellis 1965). Arthrinium malaysianum is the second species collected from the same source, namely Macaranga hullettii stems colonised by ants in Malaysia (see CBS 102052).

Arthrinium marii Larrondo & Calvo, Mycologia 82: 397 (1990).

(Fig. 9)

Fig. 9
figure9

Arthrinium marii (CBS 497.90). A. Colony on PDA. B, F. Conidiogenous cells giving rise to conidia. C–E. Elongated conidia (sterile cells?). G. Lenticular conidia in side view. H. Globose to ellipsoid conidia in surface view. Bars = 10 µm; B = C, D = E.

Type: Spain: Barcelona, from beach sand, Nov. 1990, J.V. Larrondo & A. Calvo (IMI 326872 — holotype; CBS 497.90 = MUCL 31300 — ex-type culture).

Description: Mycelium consisting of smooth, hyaline, branched, septate, 1.5—4 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, brown, smooth, ampulliform, 5–10 × 3–4.5 µm. Conidia brown, smooth, granular, globose to elongate ellipsoid in surface view, 8–10(–13) µm diam, lenticular in side view, with pale equatorial slit, (5–)6(–8) µm diam in side view; with central basal scar, 1 µm diam. Brown, elongated cells (sterile cells?) at times intermingled among conidia.

Culture characteristics: Colonies fiat, spreading, with sparse aerial mycelium. On OA pale luteous with patches of olivaceous-grey due to sporulation. On PDA olivaceous-grey on surface, reverse smoke-grey with patches of olivaceous-grey. On MEA luteous with patches of umber, reverse sienna with patches of luteous.

Additional specimens examined: Italy: Bomarzo, Footpath Santa Lecilia, Mugana, Viterbo, on stems of Phragmites australis, 24 Nov. 2010, W. Gams (CPC 18904, 18902). — The Netherlands: on leaf of Beta vulgaris, Apr. 1957, Gerold (CBS 200.57). — Sweden: oats, Nov. 1985, C. Svenson (CBS 113535). — Hong Kong: Lung Fu Shan, on culm of Arundinaria hindsii, 30 July 1998, K. D. Hyde (CBS 114803 = HKUCC 3143).

Note: Based on the results obtained here (Figs 13), it appears that Arthrinium marii is quite a commonly occurring species on different hosts in Europe, with a single report from Hong Kong.

Arthrinium ovatum Crous, sp. nov.

MycoBank MB804343

(Fig. 10)

Fig. 10
figure10

Arthrinium ovatum (CBS 115042). A. Colony on PDA. B–E. Curved or irregularly angled or lobed sterile cells. F. Conidiogenous cells giving rise to conidia. G, H. Conidia. Bars = 10 µm; B = C–E.

Etymology: Named after the ovoid shape of its conidia.

Diagnosis: Conidia oval to broadly ellipsoid, medium brown, finely roughened, 18–20 µm diam in surface view, 12–14 µm diam in side view.

Type: Hong Kong: on Arundinaria hindsii, 10 Feb. 2004, K. D. Hyde (CBS H-21273 — holotype; CBS 115042 — ex-type culture).

Description: Mycelium consisting of branched, septate, hyaline, 3–5 µm diam hyphae, becoming brown closer to conidiogenous region. Conidiophores aggregated in black sporodochia, multiseptate, branched, to 60 µm long, 5–7 µm diam. Conidiogenous cells pale brown, smooth, aggregated, ampulliform, 7–12 × 4–6 µm, in clusters on aerial mycelium, or forming black sporodochial conidiomata on agar surface. Sterile cells terminal on hyphae, pale brown, elongated ellipsoidal to clavate, 20–35 × 10–15 µm, or somewhat curved or irregularly angled or lobed, up to 80 µm long, 5–20 µm diam. Conidia oval to broadly ellipsoid, medium brown, finely roughened, 18–20 µm diam in surface view, 12–14 µm diam in side view, with equatorial slit of lighter pigment, and central scar, 2–3 µm diam.

Culture characteristics: Colonies fiat, spreading, with moderate aerial mycelium. On MEA surface ochreous with patches of dirty white, reverse sienna. On PDA surface and reverse dirty white, with patches of umber. On OA surface dirty white with patches of olivaceous-grey, reverse iron-grey.

Notes: Based on the larger conidia, Arthinium ovatum appears to represent an undescribed species (Ellis 1965, 1976, Gjaerum 1967, Pollack & Benjamin 1969, Hudson & McKenzie 1976, Calvo & Guarro 1980, Khan & Sullia 1980, Samuels et al. 1981, von Arx 1981, Koskela 1983, Kirk 1986, Larrando & Calvo 1990, 1992, Müller 1992, Bhat & Kendrick 1993, Hyde et al. 1998, Jones et al. 2009, Singh et al. 2012).

Arthrinium phaeospermum (Corda) M.B. Ellis, Mycol. Pap. 103: 8 (1965)

Basionym: Gymnosporium phaeospermum Corda, Icon. fung. 1: 1 (1837).

Synonym: Botryoconis sanguinea Tubaki, Nagaoa 1: 7 (1952).

(Fig. 11)

Fig. 11
figure11

Arthrinium phaeospermum (CBS 142.55). A. Colony on OA. B, C. Conidiogenous cells giving rise to conidia. D, E. Conidia in surface and side view. F. Conidia and sterile cells. Bars = 10 µm; B = C, D = E.

For further synonyms see Ellis (1965).

Description: Mycelium consisting of smooth, hyaline, branched, septate, 3–4 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, medium brown, smooth, ampulliform, 5–10 × 3–5 µm, apical neck 2–4 µm long, basal part 3–6 µm long. Conidia brown, smooth, granular, globose to ellipsoid in surface view, (9–)10(–12) µm diam, lenticular in side view, with pale equatorial slit, 6–7 µm diam in side view; with central basal scar, 2 µm diam.

Culture characteristics: Colonies fiat, spreading, with sparse aerial mycelium. Surface iron-grey on OA and MEA, iron-grey with patches of dirty white and sienna on PDA.

Specimens examined: Iran: Marand, on leaf of Hordeum vulgare, B. Askari, CBS 114314, 114317, 114318; Shabestar, on leaf of Hordeum vulgare, B. Askari, CBS 114315. — Japan: Tiba Prefecture: soil, 1951, K. Tubaki (CBS 142.55 — isotype of Botryoconis sanguinea).

Notes: Although Arthrinium phaeospermum is common and widely distributed, many isolates in the literature have been incorrectly identified as representing this taxon. The present phylogenetic data show that A. phaeospermum represents a species complex, and that minute differences in conidial dimensions correlate with distinct taxa. Singh et al. (2012) incorrectly cite the isotype strain of Botryoconis sanguinea as isotype of A. phaeospermum, a species to which B. sanguinea is synonymous. Although we accept the same clade as representative of A. phaeospermum, this species presently does not have any ex-type strains available for study, and needs to be epitypified.

Arthrinium phragmites Crous, sp. nov.

MycoBank MB804344

(Fig. 12)

Fig. 12
figure12

Arthrinium phragmites (CPC 18900). A. Ascoma with oozing ascospores. B. Colony on OA. C–E. Asci with ascospores. F–H. Conidiogenous cells giving rise to conidia. I, J. Conidia. Bars = 10 µm; C = D, F = G, H.

Etymology: Named after the host from which it was isolated, Phragmites.

Diagnosis: Conidia brown, smooth, but finely roughened on surface, ellipsoid to ovoid, 9–10(–12) µm in surface view, (5–)6(–7) µm in side view. Ascospores apiosporous, basal cell smaller, hyaline, straight to curved, smooth, lacking mucilaginous sheath, 22–25 × 7–9 µm; basal cell 4–6 µm long.

Type: Italy: Viterbo Province: Bomarzo, footpath from Santa Cecilia to Nugnano, on culms of Phragmites australis, 24 Nov. 2010, W. Gams (CBS H-21267 — holotype; CPC 18901, 18900 = CBS 135458 — ex-type culture).

Description: Occurring on dead stem stalks. Mycelium consisting of hyaline, smooth, branched, septate, 2–3 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells erect, ampulliform to doliiform, pale brown, smooth, 12–15 × 3–5 µm. Conidia brown, smooth to finely roughened, ellipsoid to ovoid, with equatorial slit of paler pigment, 9–10(–12) µm in surface view, (5–)6(–7) µm in side view. Sterile cells forming on solitary loci on hyphae, brown, finely roughened, ellipsoid to clavate, 13–15(–17) × (5–)6 µm. Ascomata immersed beneath a pseudostroma, 1–3 mm long, 0.5–1 mm diam, dark brown to black, becoming erumpent, splitting along its length, revealing a row of separate, subglobose, brown ascomata, each exuding a white cirrhus of ascospores; ascomata subglobose, arranged in rows, medium to dark brown, 150–200 µm diam, 200–300 µm tall; wall consisting of 3–4 layers of textura angularis; ostiole single, central, 10–25 µm diam, with a periphysate channel 20–40 µm long. Paraphyses intermingled among asci, not very prominent, hyphae-like, hyaline, smooth, septate, sparingly branched, thin-walled, up to 4 µm diam, at times breaking into segments. Asci hyaline, smooth, clavate with a short basal pedicel, unitunicate, thin-walled, obtusely rounded apex lacking an apical mechanism, 70–110 × 17–25 µm. Ascospores hyaline, smooth, 2–3-seriate, apiosporous, straight to curved, ellipsoid to reniform, some ascospores showing remnants of mucoid sheath covering length of spore; ascospores granular or not, widest in middle of apical cell, (20–)22–24(–25) × (7–)8–9(–10) µm; basal cell obtusely rounded, hyaline, smooth, 5–6 × 5 µm.

Culture characteristics: Colonies fiat, spreading, with moderate aerial mycelium. On PDA surface dirty white with patches of pale luteous, reverse luteous.

Notes: Based on its conidial dimensions, Arthrinium phragmites is close to A. phaeospermum, which has conidia that are 9–12 µm diam in surface view, and 6–7 µm diam in side view. However, conidia of A. phragmites are somewhat narrower in side view, and more ellipsoid in shape. The ascospores are also smaller than those attributed to Apiospora sinensis, the purported sexual morph of Arthrinium phaeospermum (see below). Many published reports of A. phaeospermum may however belong to A. phragmites.

Arthrinium pseudosinense Crous, sp. nov.

MycoBank MB804347

(Fig. 13)

Fig. 13
figure13

Arthrinium pseudosinense (CPC 21546). A. Erumpent ascomata on host surface. B–D. Asci and ascospores. E–H. Conidiogenous cells giving rise to conidia. Bars = 10 µm; B = C, E = F, G.

Etymology: Named after its morphological similarity to Apiospora sinensis.

Diagnosis: Conidia brown, smooth, ellipsoid, 8–10 × 7–10 µm diam in surface view, 7–8 µm diam in side view. Ascospores 2–3 µm seriate, apiosporous, basal cell smaller, hyaline, straight to curved, smooth, surrounded by a thin mucilaginous sheath, (25–)27–30(–33) × (6–)8(–10) µm; basal cell 3–6 µm long.

Type: The Netherlands: Utrecht: Utrecht Botanical Garden, on leaves of bamboo, 6 Oct. 2012, U. Damm (CBS H-21268 — holotype; CBS 135459 = CPC 21546, CPC 21547 — ex-type culture).

Description: Associated with leaf tip blight, occurring on dead leaf tissue. Mycelium consisting of pale brown, smooth, branched, septate, 2–3 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells ampulliform to doliiform or subcylindrical, pale brown, smooth, 5–12 × 3–5 µm. Conidia brown, smooth, ellipsoid, with equatorial slit of paler pigment, 8–10 × 7–10 µm diam in surface view, 7–8 µm diam in side view. Ascomata immersed, subepidermal becoming erumpent, solitary or arranged in linear rows, splitting epidermis via longitudinal slit; globose to subglobose, somewhat papillate, to 300 µm diam, brown, with central periphysate ostiole to 50 µm diam. Paraphyses hyaline, smooth, septate, prominently constricted at septa, 3–5 µm diam at basal part, apex frequently swollen, to 10 diam. Asci unitunicate, 8-spored, thin-walled, clavate, stipitate, apex lacking apical mechanism, 85–100 × 15–20 µm. Ascospores 2–3 seriate, apiosporous, basal cell smaller, hyaline, straight to curved, smooth, surrounded by a thin mucilaginous sheath, (25–)27–30(–33) × (6–)8(–10) µm; basal cell 3–6 µm long.

Culture characteristics: Colonies fiat, spreading. On MEA surface and reverse dirty white with patches of umber, and with sparse aerial mycelium. On OA surface moderately fluffy, with dirty white aerial mycelium. On PDA aerial mycelium sparse, surface concolorous with agar, with patches of umber, reverse umber.

Notes: Morphologically, Arthinium pseudosinense closely resembles Apiospora sinensis (ascospores (26–)31(–34) × (6–)7.6(–8.4) µm; conidia ellipsoid, 9–12 × 6–8 µm; Hyde et al. 1998), except that the ascospores are on average shorter and wider, have a less prominent sheath, and the conidia are smaller. A fresh collection of A. sinensis from China (south-west Huhei Province, Xuanen, on dead petiole of Trachycarpus fortunei) would be needed to facilitate a molecular comparison, with what is obviously a species complex, as other isolates originally identified as Apiospora sinensis in the CBS collection also clustered apart.

Arthrinium pseudospegazzinii Crous, sp. nov.

MycoBank MB804346

(Fig. 14)

Fig. 14
figure14

Arthrinium pseudospegazzinii (CBS 102052). A. Colony on PDA. B–E. Conidiogenous cells giving rise to conidia. F. Conidia. Bars = 10 µm; D = E.

Etymology: Named after its morphological similarity to A. spegazzinii.

Diagnosis: Conidia brown, guttulate, roughened, globose in surface view, lenticular in side view, (7–)8–9 µm diam in surface view, 5–6 µm diam in side view.

Type: Malaysia: Gombak, on Macaranga hullettii stem colonised by ants, Aug. 1999, W. Federle (CBS H-21276 — holotype; CBS 102052 — ex-type culture).

Description: Mycelium consisting of smooth, hyaline to pale brown, branched, septate, 3–4 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, brown, smooth, ampulliform with elongated neck, 8–13 µm long, basal part 3–5 × 3–5 µm, neck 3–7 × 1.5–2 µm. Conidia brown, guttulate, finely roughened, globose in surface view, lenticular in side view, with pale equatorial slit, (7–)8–9 µm diam in surface view, 5–6 µm diam in side view, with central scar, 1.5–2 µm diam.

Culture characteristics: Colonies fiat, spreading, with moderate aerial mycelium. On PDA surface pale luteous, reverse luteous. On OA surface dirty white with patches of olivaceous-grey, reverse olivaceous-grey. On MEA surface dirty white, with patches of grey-olivaceous, reverse olivaceous-grey.

Notes: Although conidia were observed to be fiinely roughened, they were not as rough, more globose in surface view, and were much smaller than those of Arthinium spegazzinii (5–8 × 3–6 µm; Ellis 1965).

Arthrinium pterospermum (Cooke & Massee) Arx, Gen. Fungi Spor. Pure Cult, 3rd edn: 331 (1981).

Basionym: Coniosporium pterospermum Cooke & Massee, Hedwigia 19: 90 (1880).

Synonym: Pteroconium pterospermum (Cooke & Massee) Grove, Hedwigia 55: 146 (1914).

(Fig. 15)

Fig. 15
figure15

Arthrinium pterospermum (CPC 20194). A. Sporodochium on host surface. B–F. Conidiogenous cells giving rise to conidia. G, H. Dentate conidia. Bars = 10 µm; B = C–F.

Type: Australia: Victoria: on Lepidosperma sp., Martin 778 (K (M) 179237 — holotype, ex herb. M. C. Cooke as Coniosporium pterospermum and annotated by W. G. Grove); Adelaide, on leaf of Lepidosperma gladiatum, 4 Jan. 2012, W. Quaedvlieg (CBS H-21275 — epitype designated here “MBT 175265”; CPC 20194, 20193 = CBS 134000 — cultures ex-epitype).

Description: Mycelium consisting of branched, septate, hyaline, 2–4 µm diam hyphae, becoming brown closer to conidiogenous region. Conidiophores aggregated in black sporodochia, transversely multiseptate, branched, brown, smooth, to 150 µm long, 3–5 µm diam. Conidiogenous cells lateral and terminal on conidiophores, brown, finely roughened, aggregated, doliiform to ampulliform, 5–10 × 4–5 µm. Conidia brown, finely roughened, with equatorial slit of lighter pigment, and central scar, polygonal, lobed or dentate, irregular in surface view, 15–25 µm diam; in side view, 8–10 µm diam.

Culture characteristics: Colonies fiat, spreading, with sparse aerial mycelium. On MEA surface pale olivaceous-grey, reverse olivaceous-grey. On OA surface olivaceous-grey, with patches of dirty white, reverse olivaceous-grey.

Additional specimen examined: New Zealand: Auckland, Auckland University, leaf lesion of Machaerina sinclairii, 27 Jan. 2008, C. F. Hill (CBS 123185 = 2008/423-X = CPC 15380).

Notes: From the Australian specimens available of this fungus in BRIP and VPRI, it seems that Arthinium pterospermum is common on leaves of Lepidosperma gladiatum (Cyperaceae). The decision by von Arx (1981) to dispose Pteroconium pterospermum to Arthrinium is supported by the present phylogenetic analysis (Fig. 1), which widens the circumscription of Arthrinium to also include conidia with irregular, lobed or dentate conidia.

Arthrinium sacchari (Speg.) M.B. Ellis, Mycol. Pap. 103: 11 (1965).

Basionym: Coniosporium sacchari Speg., Revista Fac. Agron. Univ. Nac. La Plata 2(19): 248 (1896).

(Fig. 16)

Fig. 16
figure16

Arthrinium sacchari (CBS 301.49). A. Colony on PDA. B–F. Conidiogenous cells giving rise to conidia. G, H. Conidia. Bars = 10 µm; D = E–G.

Description: Mycelium consisting of smooth, hyaline, branched, septate, 1.5–4 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, brown, smooth, ampulliform to doliiform, 5–12 × 2.5–4 µm; conidiogenous cells proliferating sympodially and also percurrently. Conidia brown, smooth, granular, globose in surface view, (6–)7(–8) µm diam, lenticular in side view, with pale equatorial slit, (3.5–)4 µm diam in side view; with central basal scar, 1 µm diam.

Culture characteristics: Colonies flat, spreading, with sparse aerial mycelium. Surface iron-grey on OA and MEA, umber on PDA.

Specimens examined: Indonesia: on bamboo, Feb. 1949, K. B. Boedijn & J. Reitsma (CBS 301.49). — The Netherlands: soil under Calluna vulgaris, June 1974, H. Linde (CBS 664.74). — UK: England: near Cambridge, on Phragmites australis, Oct. 1930, E. W. Mason (CBS 212.30). — Unknown country: from air, Aug. 1967, collector unknown (CBS H-8805, CBS 372.67).

Notes: Morphologically, Arthinium arundinis (syn. Apiospora montagnei) and Arthrinium sacchari are very similar, and best distinguished by the A. sacchari having wider conidiophores (1–1.5 µm) than A. arundinis (0.5 µm). Unfortunately, this feature was not useful in culture. However, based on the slightly larger conidia and wider hyphae with conidiogenous loci, we chose to apply the name A. sacchari to this clade, rather than the clade we attribute to A. arundinis.

Arthrinium saccharicola F. Stevens, J. Dept. Agric. Porto Rico 1(4): 223 (1917).

(Fig. 17)

Fig. 17
figure17

Arthrinium saccharicola (CBS 831.71). A. Colony on MEA. B-G. Conidiogenous cells giving rise to conidia. H. Globose conidia. Bars = 10 µm; B = C, D = E, F.

Description: Mycelium consisting of smooth, hyaline, branched, septate, 3–5 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, medium brown, finely verruculose, ampulliform, 5–10 × 3–5 µm, apical neck 2–4 µm long, basal part 3–6 µm long. Conidia brown, smooth, granular, globose to ellipsoid in surface view, (7–)8–9(–10) µm diam, lenticular in side view, with pale equatorial slit (at times appearing like a ridge of paler pigment), (4–)5(–6) µm diam in side view; with central basal scar, 2 µm diam.

Culture characteristics: Colonies fiat, spreading, with sparse aerial mycelium. Surface iron-grey on OA, on MEA and PDA umber, with patches of olivaceous grey.

Specimens examined: France: Landes, Seignosse, Etang d’Hardy, on dead culms of Phragmites australis, 11 June 1986, H. A. van der Aa (CBS 334.86). — The Netherlands: Dec. 1971, M. van Schothorst (RIVM, CBS H-8889, CBS 831.71); on Phragmites australis, Jan. 2011, P. W. Crous (CPC 18977); from air, Sept./Oct. 1972, H A. van der Aa (CBS 191.73); Z. Flevoland, Harderbos, on dead culms of Phragmites australis, 15 May 1983, W. Gams (CBS 463.83).

Notes: Conidial morphology and dimensions of isolates in this clade (Fig. 1) closely match those ascribed to Arthinium saccharicola. Unfortunately, no fiexuous conidiophores developed in culture, thus the width of conidiophores could not be confirmed. However, hyphae are similar in width to that observed by Ellis (1965) for this species, 2–5 µm thick, which is wider than that observed in other species of Arthrinium.

Arthrinium xenocordella Crous, sp. nov.

MycoBank MB804348

(Fig. 18)

Fig. 18
figure18

Arthrinium xenocordella (CBS 478.86). A. Colony on PDA. B–D. Conidiogenous cells giving rise to conidia. E–G. Setae intermingled among conidia on agar surface. H. Conidia. Bars = 10 µm; B = C, E = F.

Etymology: Not a member of the genus Cordella.

Diagnosis: Conidia brown, smooth, guttulate, globose to somewhat ellipsoid in surface view, lenticular in side view, (7–)9–10(–11) µm diam in surface view, 6–7 µm diam in side view. Setae erect, brown, smooth, subcylindrical, tapering in apical cell to subobtuse or obtuse apex, 1-septate, base truncate, to 100 µm tall, 5–8 µm diam.

Type: Zimbabwe: Pomongwe Cave, Matopos, soil from roadway, 21 Dec. 1985, J. C. Krug (CBS H-21274 — holotype; CBS 478.86 — ex-type cultures).

Description: Mycelium consisting of smooth to finely verruculose, hyaline to pale brown, branched, septate, 3–5 µm diam hyphae. Conidiophores reduced to conidiogenous cells. Conidiogenous cells aggregated in clusters on hyphae, brown, verruculose, globose to clavate to doliiform, 5–7 × 4–5 µm. Conidia brown, smooth, guttulate, globose to somewhat ellipsoid in surface view, lenticular in side view, with pale equatorial slit, (7–)9–10(–11) µm diam in surface view, 6–7 µm diam in side view, with central scar, 1.5–2 µm diam. Setae erect, brown, smooth, subcylindrical, tapering in apical cell to subobtuse or obtuse apex, 1-septate, base truncate, to 100 µm tall, 5–8 µm diam, straight to irregularly curved.

Culture characteristics: Colonies fiat, spreading, with moderate aerial mycelium. On PDA surface pale luteous with patches of olivaceous-grey, reverse pale luteous. On OA surface dirty white, reverse pale luteous. On MEA surface pale luteous, reverse luteous.

Additional specimen examined: Austria: Plaseckerjoch, soil, Aug 1966, M. A. A. Schipper (CBS H-8885, CBS 595.66 = MUCL 10009).

Notes: Arthrinium xenocordella is presently known from two strains, both isolated from soil. Based on morphology, A. xenocordella closely resembles A. phaeospermum, but the conidia tend to be globose to ellipsoid in surface view, and also form brown setae, which are not present in A. phaeospermum. That a species with setae clusters in Arthrinium, suggests that the generic name Cordella (Ellis 1965, Seifert et al. 2011), which has Apiospora sexual morphs (Samuels et al. 1981), should be reduced to synonymy with Arthrinium.

Discussion

The higher phylogenetic classification of Arthrinium (syn. Apiospora) has been the topic of much debate. Theissen & Sydow (1915) placed it in Dothideales, Müller & von Arx (1962) assigned it to Amphisphaeriaceae (Xylariales), and at first Barr chose Hyponectriaceae (Barr 1976), but later Lasiosphaeriaceae (Sordariales; Barr 1990). Following this debate, Hyde et al. (1998), introduced the family name Apiosporaceae to accommodate Apiospora and Appendicospora, based on the unique sexual morphology and their unusual asexual morphs (i.e. basauxic conidiophores with terminal and intercalary polyblastic conidiogenous cells, and unicellular conidia with germ slits). Data derived from a phylogenetic study (SSU and LSU rDNA) incorporating species of Apiospora and Appendicospora, led Smith et al. (2003) to conclude that Apiosporaceae represented one of seven families which, at that time could be resolved in Xylariales, namely Amphisphaeriaceae, Apiosporaceae, Clypeosphaeriaceae, Diatrypaceae, Graphostromataceae, Hyponectriaceae, and Xylariaceae. However, in the latest outline of the Ascomycota, Lumbsch & Huhndorf (2010) still list Apiosporaceae as fam. incertae sedis (Sordariomycetes). Based on the results we obtained in this study (Fig. 1), Apiosporaceae is confirmed as a family within Xylariales, and a sister to Amphisphaeriaceae.

The generic name Appendicospora (asexual morph unknown; Hyde 1995) was introduced to accommodate Apiosporella coryphae (Rehm 1913). Appendicospora chiefiy differs from Apiospora in having ascospores with bifurcate appendages. A second species, A. hongkongensis, was subsequently introduced to accommodate a taxon occurring on Livistona chinensis in Hong Kong (Yanna et al. 1997). Our results suggest, however, that although Appendicospora is a member of Xylariales, it does not belong to Apiosporaceae, but represents an as yet undefined family within the order.

The generic circumscription of Arthrinium has for some time been regarded as too narrow, ignoring the similar sexual morphology exhibited by various other asexual genera (von Arx 1981). The decision to reduce both Cordella and Pteroconium to synonymy with Arthrinium here is based on newly available molecular data (Fig. 1). From these data we can conclude that features such as conidium shape and the presence of setae do not appear to be reliable at the generic level in this complex.

We also introduce eight novel species here, most of which would have formerly been treated as belonging to Arthinium arudinis (syn. Apiospora montagnei) or Arthrinium phaeospermum, two commonly occurring species that that have evidently been too widely circumscribed morphologically. Arthrinium malaysianum and A. pseudospegazzinii are two novel co-occurring species on Macaranga hullettii from Malaysia. Species of bamboo have always been known as good substrates for Arthrinium, and three species are described from this host here: A. hydei and A. ovatum from Hong Kong, and A. pseudosinense from The Netherlands. In general most grasses and reeds appear to harbour species of Arthrinium as endophytes, and hence it is not surprizing that the additional novel species include A. kogelbergense on dead culms of Restionaceae from South Africa, and A. phragmites on Phragmites australis from Italy. Furthermore, species of Arthrinium are also commonly isolated from soil, as demonstrated by the description of A. rashikravindrii from soils in Norway (Singh et al. 2012), but also now shown to occur on diverse substrates in China, Japan, Thailand, and The Netherlands, and A. xenocordella from soil in Austria and Zimbabwe.

This study shows that isolates representing distinct species of Arthrinium can co-occur on the same substrate, meaning that links between sexual and asexual morphs need to be confirmed by DNA or the culture of single spores. Furthermore, Arthrinium species are highly variable morphologically, depending on the substrate and period of incubation, and the morphological features exhibited in vitro do not always match those observed in vivo. Fresh collections are therefore required to stablise the application of many older, well-established names. As a further complication, many well-known taxa unfortunately also appear to represent species complexes.

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Acknowledgements

We thank the technical staff, Arien van Iperen (cultures), Marjan Vermaas (photographic plates), and Mieke Starink-Willemse (DNA isolation, amplification, and sequencing) for their invaluable assistance.

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Correspondence to Pedro W. Crous.

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Crous, P.W., Groenewald, J.Z. A phylogenetic re-evaluation of Arthrinium. IMA Fungus 4, 133–154 (2013) doi:10.5598/imafungus.2013.04.01.13

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Keywords

  • Apiospora
  • Apiosporaceae
  • ITS
  • LSU
  • Ascomycota
  • Sordariomycetes
  • Systematics