Introduction

Macroscopic and microscopic morphology of sporocarps has traditionally been of great importance in identifying and describing species of fungi and classifying them into higher taxa (Bridge et al. 2005; Cao et al. 2021; Maharachchikumbura et al. 2021). The use of molecular data has challenged several proposed morphogroups. A well-studied example within Russulales (Agaricomycetes) is the convergent evolution of sequestrate fruiting bodies in the genera Lactarius and Russula. Multiple genera were erected to accommodate these sequestrate forms, but early molecular work has indicated that these genera are polyphyletic and that these sequestrate forms independently evolved multiple times within Lactarius and Russula (Miller et al. 2001; Nuytinck et al. 2003; Eberhardt and Verbeken 2004). Similar cases can be found in other genera including Agaricus, Amanita, Cortinarius, and Entoloma (Peintner et al. 2001; Co-David et al. 2009; Justo et al. 2010; Sánchez-García et al. 2020). Similarly, morphologically defined higher taxa of Ascomycota have also been challenged by molecular data (Arzanlou et al. 2007; Crous et al. 2007, 2009, 2021; Wynns 2015).

A severely understudied group of Ascomycota is the order Laboulbeniales (Laboulbeniomycetes). These fungi obligately live on the exoskeleton of arthropod hosts. They do not form a typical hyphal system but a multicellular, 3-dimensional structure called a thallus (Haelewaters et al. 2021a). More than 2300 species in 146 genera are currently recognized in Laboulbeniales. The vast majority of this diversity is described based on morphology while only a fraction has been sequenced (Haelewaters et al. 2021b). Molecular studies have presented evidence that both cryptic diversity and phenotypic plasticity are present within Laboulbeniales (Goldmann and Weir 2012; Goldmann et al. 2013; Haelewaters et al. 2018; Haelewaters and Pfister 2019; Van Caenegem et al. 2023a). This makes delineating the taxa of Laboulbeniales solely based on morphology difficult. The first molecular phylogenies of Laboulbeniales showed that several morphologically defined higher taxa are non-monophyletic. Antheridial characteristics appear to have a low systematic value, while features of the perithecium seem to be phylogenetically informative (Goldmann and Weir 2018; Haelewaters 2018).

The genus Botryandromyces was erected by Tavares and Majewski (1976) to accommodate two species that had already been described in other genera, Botryandromyces heteroceri (as Misgomyces heteroceri) (Fig. 1) and Botryandromyces ornatus (as Laboulbenia heteroceratis), which was selected as the type species of the genus (Tavares and Majewski 1976). Both species are reported on Heteroceridae, mainly Heterocerus Fabricius 1792, but also on the following related genera: Augyles Schiödte, 1866; Erus Pacheco, 1964; Lanternarius Pacheco, 1964; Littorimus Gozis, 1885; and Neoheterocerus Pacheco, 1964 (Tavares and Majewski 1976; Tavares 1985; Santamaria and Pedersen 2021). Species of Botryandromyces are characterized by (i) sessile antheridia, clustered around the spore septum; and (ii) a perithecium with three outer wall cells in two adjacent vertical tiers and four in the other two tiers (Tavares and Majewski 1976; Tavares 1985).

Fig. 1
figure 1

Laboulbenia spp. A Laboulbenia heteroceri. Reprinted from Goldmann and Weir (2018), Molecular phylogeny of the Laboulbeniomycetes (Ascomycota), Fungal Biol. 122:87–100, with permission from Elsevier. B Laboulbenia heteroceri, reproduced and edited from Tavares and Majewski (1976), with permission from Mycotaxon. C Laboulbenia slackensis, slide D. Haelew. 4155b. D Laboulbenia mairei, slide D. Haelew. 4847a. E Laboulbenia mairei, aberrant thallus from slide D. Haelew. 4197a. Indicated are the lower receptacle (cells I and II), the upper receptacle (cells III, IV, and V), and the blackened septum between the basal and suprabasal cell of the outer appendage. Scale bar = 100 µm

Full size image

In the protologue of Laboulbenia heteroceratis, Thaxter (1912) wrote that the production of sessile antheridia from proliferous cells had not yet been reported within the genus Laboulbenia. However, he stated that “the basal cells of its appendages may assume an appearance very similar to that of some of the aquatic forms on Gyrinidae.” The insertion cell of L. heteroceratis is concolorous with the surrounding cells. It also tends to divide into several smaller cells (Thaxter 1912). In contrast, the vast majority of species in Laboulbenia have a simple, blackened insertion cell. Thaxter (1912) did not include figures in his description, but L. heteroceratis is illustrated in Tavares and Majewski (1976: Fig. 2) and Goldmann and Weir (2018: Fig. 4 I).

Fig. 2
figure 2

Partial phylogeny of Laboulbeniales based on a concatenated 18S–ITS–28S dataset, with the genus Laboulbenia indicated in the red box. Laboulbenia heteroceri and L. mairei (in bold) are retrieved in a well-supported clade within Laboulbenia. Ultrafast bootstrap values (≥ 70) and posterior probabilities (≥ 0.70) are indicated above or below the branch leading to each node

Full size image

Botryandromyces heteroceri was described as Misgomyces heteroceri by Maire (1920). Species of Misgomyces have perithecia with four outer cell walls of unequal height in each vertical tier and compound antheridia (Tavares 1985). The genus Botryandromyces was erected to accommodate M. heteroceri, as it has a perithecium with different cellular organization and simple sessile antheridia (Tavares and Majewski 1976). Botryandromyces heteroceri differs from B. ornatus by showing considerable variation in the number of cells in the lower receptacle, ranging from two to eight, and even 33 in aberrant, filiform thalli. Botryandromyces ornatus always has a two-celled lower receptacle and shows a blackening on the perithecial apex, which B. heteroceri lacks (Tavares 1985; De Kesel 2009; Santamaria and Pedersen 2021).

Recent molecular work based on the small ribosomal subunit (18S) of the ribosomal RNA (rRNA) gene placed B. ornatus within Laboulbenia, which makes the latter a paraphyletic group (Goldmann and Weir 2018). The authors refrained from making taxonomic changes given their restricted sample size (one isolate of Botryandromyces, three isolates of Laboulbenia). Although morphological differences between the two genera are clear and well-defined, this result was not surprising given Thaxters’ (1912) decision to place the taxon currently accepted as B. ornatus in Laboulbenia. Haelewaters (2018) retrieved B. ornatus as a sister to the genus Laboulbenia, which was represented by 13 isolates. Also, this analysis was only based on the 18S region.

Here, based on recently collected material, we present a phylogeny incorporating new sequence data from three loci for B. heteroceri and show the placement of both species of Botryandromyces in relation to Laboulbenia.

Material and methods

Collection and identification of beetles and Laboulbeniales, and morphological study

Specimens of Heterocerus Fabricius, 1792 (Coleoptera, Heteroceridae), were captured alive in 2022 and 2023 using a light trap (160w ML) in a private garden in Herzele, Belgium. Specimens were immediately screened alive for infections with Laboulbeniales using a dissecting microscope. Infected specimens were stored in 99% ethanol, and uninfected specimens were released back into nature. Other hosts included in this study (Coleoptera, Carabidae) were sent by entomologists or collected by W.V.C. and A.D.K. using pitfall traps and by hand, from multiple localities in Belgium, Latvia, the Netherlands, Uganda, and the USA. These specimens were used to broaden the phylogenetic diversity and are also part of an ongoing study about the molecular diversity in the genus Laboulbenia. Thalli of Laboulbeniales were removed from their host at the point of attachment and mounted in permanent slides using the double-coverslip technique as described by Liu et al. (2020), with one modification: thalli were placed in a droplet of 1:1 Hoyer’s medium:glycerin mixture instead of pure Hoyer’s medium, because our Hoyer’s medium dried quickly. Mounted thalli were viewed at 200–1000 × magnification under an Olympus BH-2 microscope (Olympus, Center Valley, PA, USA). Images of thalli were made with a Nikon DS-Fi3 microscope camera mounted on an Eclipse Ni-U compound microscope (Nikon, Nelville, NY, USA), equipped with differential interference contrast optics, and processed using NIS-Elements BR 5.0.03 imaging software (Nikon). Photos were enhanced and the background was removed using cutout.pro (https://www.cutout.pro/) and figures were assembled in PowerPoint v.2306 (Microsoft, Redmont, WA, USA).

Studied slides are deposited at the Herbarium Universitatis Gandavensis (GENT) and Meise Botanic Garden Herbarium (BR). Hosts are stored in the Taxon Expeditions collection (TXEX) and the personal collection of Oscar Vorst.

DNA extraction, PCR amplification, and sequencing

DNA extractions were done using the REPLI-g Single Cell Kit (Qiagen, Stanford, CA, USA). All steps were performed wearing disposable latex gloves. Thalli of Laboulbeniales were removed from their host using a hypodermic needle, which was inserted into a glass syringe for holdfast, under a dissecting microscope. Removed thalli were placed in a droplet of glycerin on a microscope slide. The thalli were cut into multiple smaller pieces with the sharp tip of the needle. These pieces were placed in 0.2-ml PCR tubes with 4 µl of phosphate-buffered saline (PBS). Next, we followed the instructions as indicated in the manufacturer’s manual (Qiagen).

The small subunit (18S), the internal transcribed region (ITS), and the large subunit (28S) of the ribosomal RNA gene were amplified, using primer pairs NSL1/NSL2 for 18S (Haelewaters et al. 2015); ITS1f/ITS4 and ITS3/ITS4 for ITS (White et al. 1990; Gardes and Bruns 1993); and LR0R/LR5, NL1/NL4, and LIC24/LR3 for 28S (Vilgalys and Hester 1990; Hopple 1994; Kurtzman and Robnett 1997; Miadlikowska and Lutzoni 2000). PCR reactions (25 µl total) consisted of 13.3 µl of RedExtract Taq polymerase (Sigma-Aldrich), 2.5 µl of each 10 µM primer, 5.45 µl of ddH2O, and 1 µl of DNA extract. PCR conditions followed those from Van Caenegem et al. (2023b). Gel electrophoresis was performed and PCR products were visualized using ethidium bromide staining. Purification of successful PCR products was done using 1.5 µl of Exo-FAP (0.5 µl exonuclease I, 1 µl FAST alkaline phosphatase) (Thermo Fisher Scientific, Waltham, MA, USA) per 10 µl of PCR product, at 37 °C for 15 min, followed by deactivation at 85 °C for 15 min. The purified PCR products were sequenced at Macrogen (Amsterdam, The Netherlands) using an automated ABI 3730 XL capillary sequencer (Life Technology, Carlsbad, CA, USA). Forward and reverse sequence reads were assembled and edited in Sequencher version 5.4.6 (Gene Codes Corporation, Ann Arbor, MI, USA).

Phylogenetic analyses

We used a broad selection of newly generated Laboulbenia sequences, supplemented with 18S and 28S sequences of Laboulbenia spp. and 18S sequences of other genera downloaded from NCBI GenBank. Accession numbers of sequences and additional information about the isolates can be found in Table 1. As outgroup, we used taxa from family Dimorphomycetaceae (Dimeromyces, Nycteromyces, and Polyandromyces) (Goldmann and Weir 2018).

Table 1 Details of all isolates used in this study
Full size table

We aligned 18S and 28S sequences by locus with the G-INS-i strategy and ITS with the E-INS-i strategy using the online version 7 of MAFFT (Katoh et al. 2005, 2019; Kuraku et al. 2013). Sequences were manually trimmed using BioEdit Sequence Alignment Editor version 7.2.6 (Hall 1999) and combined in SequenceMatrix 1.9 (Vaidya et al. 2011) to construct one concatenated dataset (18S–ITS–28S). The final dataset included five partitions: 18S, the ITS1 and ITS2 spacer regions, the 5.8S gene, and 28S. Models for nucleotide substitution were selected for each partition with ModelFinder (Kalyaanamoorthy et al. 2017) according to the corrected Akaike information criterion (AICc). A maximum likelihood (ML) reconstruction was inferred using IQ-TREE (Nguyen et al. 2015) under partitioned models (Chernomor et al. 2016). Ultrafast bootstrapping was performed with 1000 replicates (Hoang et al. 2017).

Bayesian inference was done using MrBayes (Ronquist et al. 2012), available on the CIPRES Science Gateway web portal (Miller et al. 2010). Four Markov chains were run for 80 million generations, sampling every 8000 generations. Our concatenated dataset (18S–ITS–28S) was not partitioned. The analysis was performed using the GTR substitution model, with some sites being invariable and gamma-distributed rate variation across the remaining sites (GTR+I+G) (Abadi et al. 2019). A burn-in of 8000 trees was selected.

Phylogenetic trees were visualized in FigTree version 1.4.4 (http://tree.bio.ed.ac.uk/software/figtree/) and edited in Inkscape (http://www.inkscape.org).

Results

The concatenated 18S–ITS–28S dataset included 2929 characters for 39 taxa. For the maximum likelihood analysis, selected models for each partition in the concatenated dataset were GTR+F+I+G4 (18S, 1079 bp, -lnL = 11593.620), TPM2+F (ITS1, 352 bp, -lnL = 2028.319), K3P+I (5.8S, 129 bp, -lnL = 452.282), GTR+F+G4 (ITS2, 400 bp, -lnL = 4627.979), and GTR+F+I+G4 (28S, 969 bp, -lnL = 6939.442). The reconstructed Bayesian phylogeny of Laboulbeniales including the genera Botryandromyces and Laboulbenia is shown in Fig. 2 (concatenated 18S–ITS–28S dataset). The topologies of both trees resulting from the maximum likelihood and Bayesian analyses were identical. The genus Laboulbenia has high support (99/1), and the two species of Botryandromyces form a supported clade (92/0.79) within Laboulbenia. Together with L. clivinalis and L. slackensis, they form a well-supported clade (89/0.99).

The 18S sequence of B. heteroceri (D. Haelew. 4197b) shares 98.57% identity with B. ornatus (AW821) and 95.13–98.57% identity with other species of Laboulbenia, with L. collae, L. notiophili, L. pedicellata, and L. thaxteri as the highest ranked ones. To compare these results with the divergence in the 18S region among species of Laboulbenia, we blasted an 18S sequence of L. slackensis, which shares between 100% (L. slackensis) and 95.50% (L. cf. dorstii) identity. The ITS sequence of B. heteroceri is highly divergent compared to those of Laboulbenia species, with a query cover of only 21–37% (which roughly corresponds to the conserved 5.8S region and the beginning of ITS2). It shares between 91.43 and 96.89% with other species of Laboulbenia, with L. clivinalis, L. littoralis, L. pedicellata, and L. slackensis as the highest ranked. The 28S sequence of B. heteroceri shares between 81.74 and 87.44% identity with other species of Laboulbenia, with L. benjaminii, L. slackensis, and L. pedicellata as the highest ranked. To compare these results with the divergence in the 28S region among species of Laboulbenia, we blasted a 28S sequence of L. slackensis, which shares between 100% (L. slackensis) and 83.92% (L. oioveliicola) identity.

Taxonomy

Laboulbenia Mont. & C.P. Robin, in Robin, His Nat Vég Paras Paris: 622 (1853), emend. Van Caenegem & Haelew. (hoc opus)

= Botryandromyces I.I. Tav. & T. Majewski, Mycotaxon 3: 195 (1976)

= Ceraiomyces Thaxt., Proc Am Acad Arts Sci 36: 410 (1900)

= Eumisgomyces Speg., Anal Mus Nac Hist Nat B Aires 23: 176 (1912)

= Laboulbeniella Speg., Anal Mus Nac Hist Nat B Aires 23: 188 (1912)

= Scalenomyces I.I. Tav., Mycol Mem 9: 313 (1985)

= Schizolaboulbenia Middelh., Fungus Wagening 27: 73 (1957)

= Thaxteria Giard, C R Hebd Séanc Mém Soc Biol 44:156 (1892)

Description: Mostly monoecious, rarely dioecious. Receptacle typically five-celled. Primary or lower receptacle consisting of two superposed cells (I and II), or composed of a uniseriate row of multiple cells. Cell II supporting on one side the perithecial stalk cell (VI) and on the other side the secondary or upper receptacle. Secondary or upper receptacle, or androstichum, typically consisting of three cells (III, IV, and V), but can be undivided (III+IV+V) or partially divided. First cell of the appendage (insertion cell) usually flattened and more or less blackened, distinguished from surrounding cells. If not flattened and blackened, then not distinguishable from the surrounding cells and surrounded by proliferating cells. Appendages variable: simple to highly branched; short to long; with or without blackened septa; hyaline, colored, or blackened; typically consisting of an inner, usually fertile, appendage and an outer, sterile, appendage. Antheridia terminal or lateral simple phialides and then usually born on the inner appendage, rarely sessile. Solitary perithecium at least free at the ventral side, with four tiers, typically with four outer wall cells of usually unequal to rarely equal size in each vertical tier or with two tiers with four unequal wall cells and two tiers with three unequal wall cells. Edited from descriptions by Tavares (1985), Majewski (1994), and Santamaria and Pedersen (2021).

Type species: Laboulbenia rougetii Mont. & C.P. Robin.

Laboulbenia heteroceri Thaxt. (as “heteroceratis”), Proc Amer Acad Arts 48: 207 (1912)

Fig. 1A, B

≡ Botryandromyces heteroceri (Thaxt.) I.I. Tav. & T. Majewski (as “heteroceratis”), Mycotaxon 3: 195 (1976)

≡ Botryandromyces ornatus I.I. Tav., Mycol Mem 9: 156 (1985)

Laboulbenia mairei Van Caenegem & Haelew., nom. nov.

Fig. 1D, E

MycoBank number: MB 849899

Replaced synonym: Misgomyces heteroceri Maire, Bull Soc Hist Nat Afr Nord 11: 159 (1920), non Laboulbenia heteroceri Thaxt. (1912)

≡ Botryandromyces heteroceri (Maire) I.I. Tav. & T. Majewski, Mycotaxon 3: 196 (1976)

Etymology: Named after René Charles Joseph Ernest Maire, a French botanist and mycologist who made significant contributions to Laboulbeniales from France and North Africa.

Material examined: Belgium, East Flanders, Herzele, 50° 51′ 19.4″ N 3° 53′ 14.3″ E, 2 September 2022, on Heterocerus fenestratus (Thunberg, 1784) (Coleoptera, Heteroceridae), leg. W. Van Caenegem, in coll. TXEX, slides D. Haelew. 4197a (GENT:GENTFL00780, 1 aberrant thallus from right elytron) and D. Haelew. 4197c (GENT:GENTFL00781, 5 aberrant thalli from right elytron); ibid., isolate D. Haelew. 4197b (2 aberrant thalli from right elytron), GenBank accession nos. ab123456 (18S), ab123456 (ITS), and ab123456 (28S); ibid., 22 August 2023, on Heterocerus sp., leg. W. Van Caenegem, in coll. TXEX, slide D. Haelew. 4847a (GENT, 2 adult thalli from left elytron). The Netherlands, Groningen, Lauwersoog, Marnewaard, 53° 24′ N 6° 15′ E, brackish lake, 6 June 1998, on Heterocerus obsoletus Curtis, 1828 (Coleoptera, Heteroceridae), leg. O. Vorst, in coll. Vorst, slides D. Haelew. 073a (BR MYCO 173770–43, 2 adult thalli from pronotum), D. Haelew. 073b (GENT:GENTFL01154, 3 adult thalli from dorsal head), D. Haelew. 073c (GENT:GENTFL01155, 2 adult thalli from right elytron), and D. Haelew. 073d (GENT:GENTFL01156, 1 adult thallus from right elytron); North Holland, De Cocksdorp, Polder Wassenaar, 53°10’N 4°52’E, brackish ditch, 18 May 1996, on H. obsoletus, leg. O. Vorst, in coll. Vorst, slides D. Haelew. 030b (GENT:GENTFL01152, 1 adult thallus from left antenna) and D. Haelew. 030c (GENT:GENTFL01152, 1 adult thallus from right elytron).

Discussion

Here, we show that the genus Laboulbenia is paraphyletic if B. heteroceri and B. ornatus are retained in a separate genus. Therefore, we propose to synonymize Botryandromyces with Laboulbenia and to transfer B. ornatus and B. heteroceri to Laboulbenia as L. heteroceri and L. mairei, respectively. When Botryandromyces was erected, Tavares and Majewski (1976) combined two species in the genus, as B. heteroceratis (Thaxt.) I.I. Tav. & T. Majewski and B. heteroceri (Maire) I.I. Tav. & T. Majewski. As both fungal names refer to the host genus Heterocerus, the correct epithet should be “heteroceri”; “heteroceratis” is an orthographic variant (Turland et al. 2018: Art. F.9). Therefore, Tavares (1985) changed the name of B. heteroceri (Thaxt.) I.I. Tav. & T. Majewski (as “heteroceratis”) to B. ornatus. Because we reinstated L. heteroceri Thaxt., B. heteroceri based on Misgomyces heteroceri needed a replacement name in Laboulbenia: Laboulbenia mairei.

Laboulbenia mairei is positioned on a long branch in our phylogenetic tree (Fig. 2). This is mainly due to the divergence in sequences of the ITS and 28S regions between L. mairei and other species in the genus. For L. heteroceri, however, only one sequence is available: that of the conserved 18S region (Goldmann and Weir 2018). This explains the large evolutionary distance between L. heteroceri and L. mairei on the one hand and the shorter distances between L. heteroceri and closely related species of Laboulbenia on the other hand. Also, a few other species are found on relatively long branches in our phylogenetic reconstruction: Laboulbenia bicornis, L. bruchii, and L. fasciculata. This can, in part, be attributed to taxon sampling error. Indeed, only 14 of the 667 currently accepted species of Laboulbenia (Haelewaters et al. 2023) are included in our phylogenetic analysis. A revision of this genus based on molecular phylogenetic data, with increased sampling, both taxonomically (more taxa) and geographically (from a wide geographic coverage), is desirable and may result in the disintegration of Laboulbenia in meaningful taxonomic groups (sections, subgenera, or different genera). We conclude that the proposed transfer of Botryandromyces species to Laboulbenia is on par with our current morphological and molecular knowledge of the genus.

A few considerations arise after including these species in the genus Laboulbenia. The difference in perithecial outer wall cells is striking. The number of outer wall cells in each tier is a commonly used and reliable character to delineate and identify genera of Laboulbeniales (Tavares 1985; Majewski 1994; De Kesel et al. 2020; Santamaria and Pedersen 2021). The difference in the number of these cells was one of the main reasons why Tavares and Majewski (1976) erected Botryandromyces. Tavares (1985) proposed that it “was undoubtedly derived from a more typical arrangement of four cells in each row.” In addition, Tavares (1985) erected Dixomyces and Scalenomyces to accommodate a few other species, based on the number of outer wall cells in each tier and characteristics of the appendages and the receptacle. Eventually, Rossi and Santamaria (2008) synonymized Scalenomyces with Laboulbenia, as the morphology of their newly described L. magrinii was similar to S. endogaea. Both species are known from endogean ground beetles (Coleoptera, Carabidae). Whether their specific morphology is an adaptation to their host, their host’s ecology, the environment, due to random genetic drift, or other factors, is unknown. Similar thoughts can be made regarding morphological changes of L. heteroceri and L. mairei compared to phylogenetically related species (Fig. 2). Both species are found on Heteroceridae, while L. clivinalis and L. slackensis are found on Carabidae, like most species of Laboulbenia are. Our phylogeny provides evidence for a host shift, which might have driven the observed changes in morphology.

Remarkably, the lower receptacle of L. mairei often shows secondary divisions, while L. heteroceri consistently has a two-celled lower receptacle (Fig. 1) (Thaxter 1912; Maire 1920; Tavares and Majewski 1976). The receptacle of L. heteroceri resembles that of a typical species of Laboulbenia, which was already acknowledged by Thaxter (1912). Laboulbenia mairei is not the only species in the genus that has more than two cells in the lower receptacle. Laboulbenia dohrni and L. partita also have this peculiar organization of the lower receptacle but differ in other characteristics, e.g., they have a typical blackened insertion cell (Thaxter 1914; Spegazzini 1915; Tavares 1985). In L. mairei, the number of cells in the lower receptacle is variable and may depend on the position of thalli on the host integument or thallus age (Majewski 1994; De Kesel 2009; Santamaria and Pedersen 2021). Thalli of L. mairei with a typical Laboulbenia receptacle are illustrated by Majewski (1994).

The upper receptacle of L. heteroceri and L. mairei is reminiscent of the ones from species in the Laboulbenia luxurians group as defined by Tavares (1985). Similar to the species in this group, the height of their cells IV and V is equal; the vertical septum between these cells reaches cell III. Laboulbenia clivinalis and L. slackensis also belong to this group and form a well-supported clade with L. heteroceri and L. mairei in our phylogeny (Fig. 2). In addition, most species of this group (e.g., L. clivinalis and L. slackensis) have a blackened septum between the basal and suprabasal cells of their outer appendage. Laboulbenia heteroceri also has a blackened septum in this position (Fig. 1). Species in this group are commonly found on hosts that live in humid environments like sandy or muddy river banks, seashores, and wet grasslands. Carabidae (hosts for L. clivinalis, L. pedicellata, and L. slackensis) and Heteroceridae (hosts for L. heteroceri and L. mairei) are often found together in these environments (Holeski and Graves 1978; A. De Kesel, pers. obs.). This shared habitat preference makes host shifts of Laboulbeniales between those two families likely (Rossi 2011; De Kesel and Haelewaters 2014).

The morphology of Dixomyces clivinae and D. pallescens is similar to that of L. heteroceri and L. mairei. They were transferred from Laboulbenia in which they were originally described by Thaxter (1896, 1908) to Dixomyces by Tavares (1985). Both Dixomyces species were described from carabid beetles, suggesting that the adjusted morphology was already present on carabid hosts. No sequence data of these species are available, but we hypothesize that D. clivinae and D. pallescens may also need to be transferred back to Laboulbenia.

Thaxter (1912) reported morphological differences between the holotype of L. heteroceri from Argentina and thalli found on beetles collected in KS, USA. Several studies also reported differences in length between the holotype of L. mairei from Algeria and specimens from Europe. Reasons behind these differences are unknown but they have been attributed to either inaccurate measurements or environmental differences (Scheloske 1969; Tavares and Majewski 1976; Majewski 1994; Weir 1994). Given that cryptic diversity in Laboulbeniales is proven using molecular data (Haelewaters et al. 2018, 2019) and that both L. heteroceri and L. mairei are reported from different genera of Heteroceridae, it is only a matter of time and effort to confirm or reject whether there are multiple cryptic species hidden under these two names. Host specimens should be freshly collected to sequence species of Dixomyces and Scalenomyces, L. heteroceri, and L. mairei and resolve these outstanding taxonomic issues.

Conclusions

Based on molecular phylogenetic data, we synonymized Botryandromyces with Laboulbenia and emended the description of Laboulbenia to include that (1) the perithecial outer wall can have either four cells in each of the four vertical tiers, or two tiers with four cells and two tiers with three cells, and (2) the lower receptacle can be either two-celled or multi-celled. The species formerly placed in Botryandromyces (now known as Laboulbenia heteroceri and L. mairei) are morphologically similar to species of the Laboulbenia luxurians species group. Their hosts also occupy the same habitats, which increases the chance of a host shift. Although there is a major difference in the morphology of the perithecium, the equal size of cells IV and V and the presence of a blackened septum in the outer appendage correspond to their phylogenetic position inside this species group. Future research should focus on adding sequence data for morphologically described genera related to Laboulbenia, host shifts within the L. luxurians species group, and cryptic diversity in L. heteroceri and L. mairei.