Five new species in the Tremella caloplacae complex

Abstract

Tremella caloplacae (Zahlbr.) Diederich is a species complex including at least nine different species. Here, we formally describe the new species Tremella elegantis, T. nimisiana, T. parietinae, T. pusillae and T. sorediatae. Tremella elegantis induces galls in the hymenium of Rusavskia elegans and forms 2-celled basidia, where cells rarely elongate and sometimes give the appearance of two immature, independent basidia. Tremella nimisiana has small basidiomata (less than 1 mm diam.), narrowly ellipsoid to pyriform 2-celled, occasionally clavate to subcylindrical 3-celled basidia, and grows in the hymenium of Xanthocarpia species. Tremella parietinae is characterized by the exclusive growth in the hymenium of Xanthoria parietina, the broadly fusiform to ellipsoid probasidia, and the subspherical, pyriform or ellipsoid 2(–3)-celled basidia. Tremella pusillae has ellipsoidal probasidia, 2(–3)-celled pyriform or ellipsoidal basidia that sometimes are constricted at the septum, and grows only on Calogaya pusilla. Tremella sorediatae is characterized by inducing galls on the thallus of Rusavskia sorediata and by pyriform to ellipsoid basidia that sometimes are constricted at the septum. Three species are not formally described and are left unnamed as Tremella sp. 13 on Calogaya biatorina, Tremella sp. 14 on Calogaya decipiens and Tremella sp. 15 on Polycauliona sp. Tremella caloplacae in the strict sense is re-circumscribed as a species confined to Variospora species.

Introduction

Tremella Pers. (Tremellales, Agaricomycotina) is a widespread genus with more than 300 species that grow associated with other fungi, including lichenized fungi. Lichenicolous Tremella species were neglected and poorly studied until the publication of the first monograph on lichenicolous heterobasidiomycetes by Diederich (1996). Since then, the number of formally described lichenicolous species has increased to 117, and we expect this number to continue increasing in the coming years (Diederich et al. 2022). Species delimitation is often complicated in this group due to the scarcity of morphological characters (Diederich 1996). Still, lichenicolous Tremella species are highly specific towards their hosts, usually growing on a single species or genus (Diederich et al. 2018), which has been useful for species circumscription (Diederich 1996; Millanes et al. 2015; Zamora et al. 2016; Diederich et al. 2022). Evidence suggests that speciation is driven by host selection rather than by geographical isolation (Werth et al. 2013; Millanes et al. 2014, 2015, 2016; Diederich & Ertz 2020; Diederich et al. 2022).

A large amount of still overlooked diversity in lichenicolous tremellalean fungi is hidden in several species complexes (Diederich et al. 2022). Tremella caloplacae (Zahlbr.) Diederich was first described as a hyphomycete with large, 1-septate conidia (as Lindauopsis caloplacae Zahlbr.; Zahlbruckner 1906). The description was based on a specimen growing in the hymenium of Caloplaca callopisma (Ach.) Th. Fr. (currently Variospora aurantia (Pers.) Arup et al.), collected in Crete. In his monograph of lichenicolous heterobasidiomycetes, Diederich (1996) described a species of lichenicolous Tremella growing in the hymenium of specimens of Caloplaca collected in Austria and Great Britain, but he left the species unnamed as Tremella sp. 1 due to the lack of taxonomically useful morphological characters of the specimens and the impossibility of finding differences between this species and Tremella rinodinae Diederich & M.S. Christ. The species was not formally described until 2003 (Sérusiaux et al. 2003), when enough material from new localities had been collected and studied. Sérusiaux et al. (2003) studied the type of Lindauopsis caloplacae Zahlbr. and concluded that the structures that Zahlbruckner (1906) illustrated in great detail (and interpreted as conidia) in reality correspond to tremelloid basidia with one transverse primary septum. The species corresponds to ‘Tremella sp. 1’ (sensu Diederich 1996) and was combined in Tremella and reported on several species of Caloplaca s. lat. by Sérusiaux et al. (2003). Later, Diederich (2007) reported the species growing on Xanthoria sorediata (Vain.) Poelt from Canada and Greenland. The two collections on X. sorediata could not be distinguished microscopically from the material on Caloplaca s. lat., although they were macroscopically very distinct. That led Diederich (2007) to suggest that Tremella caloplacae could represent a species complex needing further study, also considering the polyphyly of both Caloplaca and Xanthoria, which was already acknowledged at that time by Gaya et al. (2003). The first molecular data obtained from Tremella caloplacae also supported this hypothesis (Millanes et al. 2011), although this was not discussed by those authors.

Freire-Rallo et al. (2023) studied the phylogenetic relationships and species boundaries of 52 specimens of Tremella caloplacae s. lat. growing on different hosts of the Teloschistaceae. That study showed that Tremella caloplacae s. lat. is indeed a species complex including at least six putative new species, each of them restricted to grow and develop on a single host species or genus. The specimens analyzed in Freire-Rallo et al. (2023), to which we refer here for practical reasons as the Tremella caloplacae species complex, are studied in this work at a morphological level. In addition, we have sequenced two specimens of Tremella growing on Calogaya biatorina (A. Massal.) Arup et al. and on Polycauliona sp., and these are also included in this study to test their phylogenetic position.

The aim of this work is to formally describe five species and to tentatively describe three other species within the Tremella caloplacae complex, combining morphological, ecological and molecular data, and studying the phylogenetic relationships within the group.

Materials and Methods

Morphological studies

Specimens studied are housed in the ANGUC, BR, GZU, MARSSJ, S and UBC herbaria (abbreviations according to Index Herbariorum http://sweetgum.nybg.org/science/ih/) or the private collection of Javier Etayo (Table 1). Macroscopic characters were observed using an Olympus SZX16 or a Leica MZ 7.5 dissecting microscope. Images of macroscopic traits were captured with either a Sony Alpha A6000 camera on an Olympus SZX16 dissecting microscope or a Canon 6D camera with Nikon BD Plan 5 or 10 microscope objectives, using StackShot (Cognisys) and Helicon Focus (HeliconSoft) for increasing the depth of field. The samples were first moistened with distilled water and then the surface of the gall cut with a razor blade to maximize the amount of tremellalean hyphae taken. Sections were pretreated with a solution of KOH (5%) and stained with phloxine B (1% in water), following the methods used by Diederich (1996). Microscopic photographs were captured with a Sony Alpha A6000 or an Olympus DP23 camera on an Olympus BX51 microscope, or a Leica EC3 camera on a Leica DMLB microscope, without or with DIC optics. Values of the measured structures were rounded to the nearest 0.5 μm. The basidiospore apiculus is not included in the measurements. Microscopic images were adjusted with Helicon Focus to increase the depth of field. Measurements are presented with a range representing the 69% probability interval; within parentheses the smallest and largest measurements are specified followed by the mean (x̄) minus and plus the standard deviation (SD) as follows: (min–) (x̄ − SD) – (x̄ + SD) (–max). Basidiospore length/width ratio is expressed as Q. The total number of measurements (n) is given within parentheses. Mycological terminology used follows Diederich (1996), Kirk et al. (2008) and Diederich et al. (2022).

Table 1. Tremella sequences newly generated in this study (bold), or downloaded from GenBank, with specimen data. Type specimens are indicated by ‘(T)’.

Molecular studies

DNA extraction, amplification and sequencing

DNA was extracted directly from the specimens studied (Table 1), either freshly collected or herbarium material. Total DNA extraction was performed using the Qiagen DNeasy Plant Mini Kit, following the manufacturer's instructions but repeating the final elution of 50 μl with water twice.

For PCR amplification, we combined general fungal primers with others specifically designed to amplify DNA from the tremellalean fungi (Millanes et al. 2011; Freire-Rallo et al. 2023). To perform the PCRs, we used the primers ITS1F (Gardes & Bruns 1993), BasidLSU3-3 (Millanes et al. 2011) and TRMcal_R2 (Freire-Rallo et al. 2023) to amplify the internal transcribed spacer I, the 5.8S rDNA gene and the internal transcribed spacer II gene. PCR reactions were carried out using Illustra^TM Hot Star PCR beads, according to the manufacturer's instructions. For ITS1F/BasidLSU3-3 and ITS1F/TRMcal_R2, we ran an initial denaturing at 95 °C for 5 min; four cycles of 95 °C for 40 s, 53 °C for 40 s and 72 °C for 90 s; four cycles of 95 °C for 30 s, 50 °C for 30 s and 72 °C for 90 s; 32 cycles of 95 °C for 30 s, 47 °C for 30 s and 72 °C for 90 s; a final extension step of 72 °C for 10 min. For PCR samples we added 2 μl of DNA extraction and 0.5 μl of each primer (primer concentration 10 μM). Before sequencing, we purified PCR products using 5 μl of Exo-sap-IT^© (USB Corporation) added to 22 μl volume of amplification product. Sequencing was performed at the Molecular Systematic Laboratory of the Swedish Museum of Natural History, at the Genomic Unit in Rey Juan Carlos University, or by Macrogen Europe (Amsterdam, the Netherlands) or Macrogen Spain (Madrid, Spain).

Sequence alignment and phylogenetic analysis

Newly produced sequences were assembled and edited with Geneious Prime® v. 2021.0.3. (https://www.geneious.com). A data matrix was produced for subsequent phylogenetic analyses using sequences of the ITS1, 5.8S, ITS2 and LSU nuclear rDNA produced by us or retrieved from GenBank (Table 1). Tremella candelariellae was used as outgroup (Table 1) based on previous literature (Millanes et al. 2011; Liu et al. 2015) and from preliminary trees. Sequences were aligned using the Q-INS-I algorithm as implemented in MAFFT v. 7 (Katoh et al. 2019). Misaligned positions, major insertions and ambiguous and/or divergent regions were identified and deleted with Gblocks v. 0.91b (Castresana 2000), following the relaxed conditions described by Talavera & Castresana (2007). Alignments were then checked with Mesquite (Maddison & Maddison 2021) and terminal gaps were converted to missing data.

We considered four independent partitions, ITS1, 5.8S, ITS2 and nuLSU, in all analyses. Each partition was analyzed individually by maximum likelihood ultrafast bootstrap (UF-BS) in IQ-TREE to assess for conflicts. Strongly supported clades (IQ-TREE UF-BS > 95%) in disagreement were considered to be an indication of significant conflict (Mason-Gamer & Kellogg 1996; Hoang et al. 2018). Since no conflict was detected in our data sets, they were combined and then analyzed using maximum likelihood (ML) and Bayesian approaches. Maximum likelihood analyses were carried out in IQ-TREE (Nguyen et al. 2015). Model selection for each partition was achieved using ModelFinder in IQ-TREE (Kalyaanamoorthy et al. 2017), with the corrected Akaike information criterion (AICc). Following this scheme, the TIM2e + I model was selected for ITS1 and 5.8S, TIM2e + Γ4 for ITS2, and TIM3 + F + Γ4 for nuLSU. We assessed node support by standard bootstrap using 1000 bootstrap pseudoreplicates. Bayesian analyses were performed by Markov chain Monte Carlo (MCMC) sampling as implemented in the software MrBayes v. 3.2.7a (Ronquist et al. 2012). Since not all models tested by ModelFinder in IQ-TREE can be directly implemented in MrBayes, for the Bayesian analyses we selected from a subsample of substitution models using the corrected Akaike information criterion (AICc) as implemented in jModelTest 2 (Darriba et al. 2012), allowing only three substitution schemes, using full likelihood optimization and four discrete gamma categories. In this case, JC was selected for ITS1 and 5.8S, and SYM + Γ for ITS2 and nuLSU rDNA. The combined analyses treated the different regions as separate partitions with topology linked across partitions but separate model parameter values and proportional rates across partitions. For each combined data set, two parallel runs were performed, each with four chains, three of which were incrementally heated with a temperature of 0.15. The analyses were diagnosed for convergence every 100 000 generations and were set to halt automatically when the average standard deviation of splits across runs in the last half of the analysis descended below 0.01. Every 100th tree was saved. The first 50% of each run was discarded as burn-in. Both ML and Bayesian analyses were performed on the CIPRES Web Portal (Miller et al. 2015).

Results and Discussion

Nine sequences of the ITS region and one sequence of the nuLSU region were newly produced for this study. The alignment included these newly generated sequences, combined with sequences of ITS and nuLSU sequenced by Freire-Rallo et al. (2023) or retrieved from GenBank (Table 1). A data matrix corresponding to the ITS and nuLSU regions was generated with a total of 1360 characters (ITS1, 1–122; 5.8S, 123–276; ITS2, 277–595; nuLSU, 596–1360). The best tree obtained from the ML analysis had a ln-likelihood value of −2998.5609. The Bayesian analysis halted after 900 000 generations, at which time the average standard deviation of split frequencies across runs was 0.0098, indicating that the three runs had converged (< 0.01). A majority-rule consensus tree was constructed from the 9000 trees of the stationary tree sample. No incongruences were found among the topologies of the trees obtained with ML and Bayesian inference and therefore only the best tree from the ML analysis is shown in Figure 1.

Figure 1. Phylogram based on ITS and nuLSU sequences of Tremella species, corresponding to the best tree recovered in the maximum likelihood analysis (ML), with information on the Bayesian posterior probability (PP) values added. Branches in bold indicate nodes supported by both PP≥ 0.95 and ML bootstrap (ML-BS) values ≥ 70. When nodes received support only from one of the two methods, ML-BS values ≥ 70 are indicated above branches and PP values ≥ 0.95, below branches. Species names are indicated in the right margin. Types are indicated with ‘(T)’. Branch lengths are scaled to the expected number of substitutions per site.

The phylogenetic analyses showed at least nine distinct lineages. Most of them coincide with the species delimitation analyses performed by Freire-Rallo et al. (2023), who discussed at least nine different species growing on different hosts: 1) on Xanthoria parietina (L.) Th. Fr., 2) on Xanthocarpia lactea (A. Massal.) A. Massal., 3) on Xanthocarpia sp., 4) on Calogaya decipiens (Arnold) Arup et al., 5) on Calogaya pusilla (A. Massal.) Arup et al., 6) on Rusavskia elegans (Link) S.Y. Kondr. & Kärnefelt, 7) on Rusavskia sorediata (Vain.) S.Y. Kondr. & Kärnefelt, 8) on Variospora sp., and 9) on Leproplaca xantholyta (Nyl.) Nyl. Not all the species delimited in Freire-Rallo et al. (2023) will be formally described in this work. The specimen of T. caloplacae s. lat. on Leproplaca xantholyta is in a very poor condition so it has not been possible to obtain sufficient morphological data for a full description. Although T. caloplacae s. lat. on Calogaya decipiens is one of the species delimited in Freire-Rallo et al. (2023), we refrain from describing a species based on a single specimen and instead leave it unnamed as Tremella sp. 14, until more specimens are available. The same applies to Tremella sp. 13 on Calogaya biatorina and Tremella sp. 15 on Polycauliona sp. The latter two samples were not included in Freire-Rallo et al. (2023) and were sequenced for the first time in this study. The specimens growing on Xanthocarpia species are all included in the newly described Tremella nimisiana, although our current and previous phylogenetic results (Freire-Rallo et al. 2023) clearly show that Tremella material growing on Xanthocarpia represents a species complex. This conservative decision was made owing to the low number of specimens available growing on each Xanthocarpia host, and to the scarcity of diagnostic characters, which makes a morphological characterization based on a small number of samples challenging.

There are also other lichenicolous Tremella species known to grow on Teloschistaceae hosts (Diederich et al. 2022): Tremella teloschistis Diederich et al., which is phylogenetically not close to Tremella caloplacae s. lat., on Teloschistes exilis; T. occultixanthoriae Diederich et al. on Xanthoria parietina; T. pisutiellae Diederich & W. R. Buck on Pisutiella conversa; T. xanthomendozae Diederich et al. on Xanthomendoza weberi (S.Y. Kondr. & Kärnefelt) L. Lindblom; and Tremella sp. 11 on Pyrenodesmia chalybaea (Fr.) A. Massal., from which there are no sequences and which is therefore not included in this work. These species are, however, included in our key to facilitate the identification of the newly described species, and to complement recently published keys (Diederich et al. 2022).

Key to Tremella species

1. 1 Basidia devoid of epibasidia; on the lower thallus surface of Xanthoria parietina ……… T. occultixanthoriae

   Basidia with epibasidia ……… 2

2. 2(1) Basidiomatal galls on the host thallus ……… 3

   Basidia immersed in the hymenium of the host ……… 5

3. 3(2) Basidiomatal galls elongated; on Teloschistes exilis ……… T. teloschistis

   Basidiomatal galls subspherical; on other hosts ……… 4

4. 4(3) Basidia transversely or obliquely septate, 5.5–9 μm wide; basidiospores 5–7.5 × 4.5–6 μm; on Xanthomendoza weberi ………… ……… T. xanthomendozae

   Basidia transversely or obliquely septate, 8.7–13 μm wide or longitudinally septate, 13.2–16.2 μm wide; basidiospores slightly smaller; on Rusavskia sorediata ……… T. sorediatae

5. 5(2) Infected apothecia without visible symptoms or only slightly swollen; basidia 2-celled, transversely septate ……… 6

   Infected apothecia strongly swollen at maturity, with convex basidiomatal galls; basidia 2-celled or rarely 3-celled ……… 7

6. 6(5) Basidia 17–24 × 7–10 μm; on Pisutiella conversa ……… T. pisutiellae

   Basidia shorter, 12–18 × 7–9 μm; on Pyrenodesmia chalybaea ……… Tremella sp. 11

7. 7(5) Basidiomata often > 1 mm diam. ……… 8

   Basidiomata < 1 mm diam. ……… 11

8. 8(7) Clamped hyphae not or rarely observed; probasidia subspherical to ellipsoidal, not fusiform ……… 9

   Clamped hyphae present; probasidia ellipsoidal to broadly fusiform ……… 10

9. 9(8) Basidia 2-celled; basidiospores 3.8–9.6 × 3.8–7.9 μm; on Variospora spp. ……… T. caloplacae

   Basidia 2-celled or rarely 3-celled; basidiospores 7.6–9.2 × 6.7–10.2 μm; on Calogaya pusilla ……… T. pusillae

10. 10(8) Basidia 2-celled or rarely 3-celled, not elongating separately; basidiospores 6.5–11.9 × 5.7–11.9 μm; on Xanthoria parietina ……… T. parietinae

    Basidia 2-celled, when longitudinally septate, cells occasionally elongating and growing separately; basidiospores smaller (one measurement of 5.5 × 6.0 μm); on Rusavskia elegans ……… T. elegantis

11. 11(7) Clamped hyphae not observed; basidia with transverse septa often constricted at the septum ……… 12

    Clamped hyphae present; basidia with transverse septa rarely constricted at the septum ……… 13

12. 12(11) Basidia 2-celled or rarely 3-celled; basidiospores 8.7–10.2 × 8.2–10.3 μm; on Calogaya biatorina ……… Tremella sp. 13

    Basidia 2-celled, when transversely septate sometimes upper part subglobose and wider than the lower part; basidiospores smaller (one measurement of 5.5 × 4.5 μm); on Calogaya decipiens ……… Tremella sp. 14

13. 13(11) Basidia 2-celled and ellipsoid to pyriform, rarely 3-celled and clavate to subcylindrical; basidiospores 7.5–10.3 × 6.9–10.1 μm; on Xanthocarpia spp. ……… T. nimisiana

    Basidia 2-celled, elongate, very narrowly ellipsoid to ellipsoid; basidiospores smaller (one measurement of 6.5 × 7.0 μm); on Polycauliona sp. ……… Tremella sp. 15

Taxonomy

Tremella caloplacae (Zahlbr.) Diederich

In Sérusiaux et al., Lejeunia n. s. 173, 31 (2003).—Lindauopsis caloplacae Zahlbr., Ber. Deutsch. Bot. Ges. 24, 145 (1906); type: Crete, ‘an Kalkfelsen bei Kristallenia’, 1904, R. Sturany (W 11196, lichenicolous fungus in apothecia of Variospora aurantia: lectotype, designated by Sérusiaux et al. (2003)).

= Tremella sp. 1, in Diederich, Bibl. Lichenol. 61, 167 (1996).

(Fig. 2)

Figure 2. Tremella caloplacae (A, I, J, M & O, lectotype on Variospora aurantia; B & E, Diederich 12328 on V. flavescens; K, T, U & W, Freire-Rallo S43 on V. flavescens; N, Freire-Rallo S37 on V. flavescens; C, D, G, L, R & S, Sérusiaux iv 1983 on V. dolomiticola; F, H, P, Q & V, Millanes 1371 & Freire-Rallo on V. dolomiticola). A–C, variation in gall morphology. D–G, probasidia showing basal clamp connections and haustoria. H–K, transversely septate basidia. L–M, obliquely septate basidia. N–P, longitudinally septate basidia. Q–S, haustoria and hyphal clamp connections. T–W, basidiospores. Scales: A–C = 1 mm; D–R = 10 μm; S–W = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, sometimes hemispherical, smooth, uniform or irregular, light yellow to brown galls in the hymenium of the host, sometimes a single gall occupying the whole surface of the hymenium obscuring the thalline margin, often scattered all over the hymenium or forming conglomerates, (0.06–)0.1–0.5(–1.8) mm diam. (n = 404). Hyphae rarely with clamp connections, thin-walled, up to 3 μm diam.; haustorial branches present, tremelloid, rarely with a bifurcated filament or with two filaments, mother cell (2–)2.7–4.8(–7) μm diam. (n = 114), filament up to 9.5 μm in length. Hymenium reduced when young but developed when old, containing numerous subspherical to ellipsoid, rarely cylindrical probasidia with a basal clamp connection. Basidia subspherical to ellipsoid, 2-celled when mature, with one transverse, sometimes oblique, rarely longitudinal septum, when transversely septate sometimes constricted at the septum, or upper part subglobose and wider than the lower part, (11–)14.5–27.2(–46) × (5.5–)8.0–21.2(–23) μm (n = 508) [transversely septate: (11–)15.6–27.2(–46) × (5.5–)8.8–14.5(–21) μm (n = 401); obliquely septate: (12.5–)14.5–25.7(–34) × (6.5–)8.0–15.8(–22) μm (n = 89); longitudinally septate: (11–)15.1–22.0(–25.5) × (9–)13.3–21.2(–23) μm (n = 18)]; epibasidia elongate, (1.5–)2.3–5.8(–8.5) μm diam. (n = 77), up to at least 37 μm in length. Basidiospores subspherical to ellipsoid, apiculus present, (3.5–)3.8–9.6(–14) × (3–)3.8–7.9(–9.5) μm (n = 13).

Ecology and distribution

Tremella caloplacae s. str. is known to grow only in the hymenium of Variospora aurantia, V. dolomiticola, V. flavescens and V. thallincola. The species is known from France, Greece, Luxembourg, Spain, Sweden, Ukraine and the United Kingdom.

Notes

The description above refers to Tremella caloplacae s. str. and is based on the description by Diederich (1996), slightly modified according to the material recently studied and the exclusion of the newly described species. Tremella caloplacae s. str. grows exclusively on Variospora spp. and differs from other species in the T. caloplacae complex by the size of the basidiomata (often > 1 mm diam.), the rarity of hyphae with clamp connections, and the subspherical to ellipsoidal probasidia. Other species growing in the hymenium of Teloschistaceae hosts are T. pisutiellae and Tremella sp. 11 (Diederich et al. 2022) but these are not known to induce galls, in contrast to the rest of intrahymenial species in the T. caloplacae complex. Species with a micromorphology resembling that of T. caloplacae s. str. (i.e. 2-celled basidia transversely, obliquely or only rarely longitudinally septate) are T. dirinariae Diederich et al., T. montis-wilhelmii Diederich and T. rinodinae Diederich & M.S. Christ. However, they differ in host selection and only T. rinodinae grows intrahymenially. The recent specimens of T. caloplacae from Crete have been collected 2.5 km NNE of the type locality and are thus likely to be genetically very similar to the type. The circumscription of Tremella caloplacae s. str. may be modified in the future when there is better knowledge of the species complex.

Additional specimens examined

France: Pas-de-Calais: Audresselles, Cran-aux-Oeufs, falaise maritime, sur rochers arénacés face à la mer, on Variospora dolomiticola, 1983, Sérusiaux (BR, LG, S). Vaucluse: 2 km S of Gordes, col de Gordes, on V. flavescens, 1995, Diederich 12328 (BR).—Great Britain: England: V.C. 3, South Devon, Torbay, Berry Head, locally abundant, on V. thallincola, 50°25ʹN, 3°32ʹW, 1997, Kärnefelt 970901 (S).—Greece: Crete: S of Malia, Lasithi Plateau, 500 m NW of Tzermiado, 35°12ʹ16ʺN, 25°28ʹ58ʺE, 890 m, on V. dolomiticola, 2016, Diederich 18575 (BR); ibid., on V. aurantia, 2016, Diederich 18576 (BR).—Luxembourg: Luxembourg City, ancient city wall S of Rumm and W of the railway bridge, 49°36ʹ28ʺN, 6°8ʹ20ʺE, 245 m, on V. flavescens, 2016, Diederich 18559 (BR).—Spain: Guadalajara: Valdegrudas, Páramos de la Alcarria Occidental, cliff next to a crop area, on V. aurantia, 40°43ʹ03ʺN, 3°00ʹ32ʺW, 962 m, 2017, Millanes 1370 & Freire-Rallo (S); ibid., on V. dolomiticola, Millanes 1371 & Freire-Rallo (S).—Sweden: Gotland: Hangvar par., Irevik, along the small road towards Svarthäll on the east side of Irevik, on V. flavescens, 57°50ʹ14ʺN, 18°36ʹ22ʺE, 2014, Westberg, Košuthová & Prieto GTL24 (S). Öland: Jordhamn, on V. flavescens, 57°5ʹ52ʺN, 16°53ʹ13ʺE, 8 m, 2017, Freire-Rallo S37 (S); ibid., Freire-Rallo S41, S42, S43, S46, S50 (S).—Ukraine: Khmel'nyts’ka Oblast: Posil's’ki Tovtry National Park, Kamyanets’-Podil's’kyi Rayon, Kitaygorod Village, 15 km SE of Kamyanets’-Podil's’kyi, canyon of Ternava River, 48°38ʹ25ʺN, 26°46ʹ59ʺE, 141 m, on V. aurantia, 2003, Kukwa 1851 (S).

Tremella elegantis Freire-Rallo, Diederich, Millanes & Wedin sp. nov.

MycoBank No.: MB 847663

Differs from Tremella caloplacae in the higher frequency of hyphae with clamp connections, the presence of broadly fusiform probasidia, the formation of basidia with longitudinal septa in which cells elongate and grow separately, and in developing only on Rusavskia elegans.

Type: Norway, Finnmark, Vadsø, Store Ekkerøya, 70°04ʹ14ʺN, 30°06ʹ26ʺE, 50 m, on calcareous rock, on Rusavskia elegans, 2014, Millanes 1113 (S—holotype). DNA voucher: AM444; GenBank Accession nos: OQ192942 (ITS), OQ176391 (LSU).

(Fig. 3)

Figure 3. Tremella elegantis on Rusavskia elegans (A, D & M, Millanes 808; B, E & F, Millanes 908; C, G, H, J, Q & P, holotype; I & L, Millanes 1085; K, N & R, Millanes 904; O, Odelvik, Hedenäs & Rönblom 14-453). A–C, variation in gall morphology. D–H, 2-celled transversely septate basidia with one haustorium. I–K, obliquely septate basidia with one haustorium. L–O, longitudinally septate basidia with haustoria. P, basidiospore. Q & R, hyphae with clamp connections. Scales: A–C = 1 mm; D–O = 10 μm; P–R = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, orange or reddish orange to brown galls in the hymenium of the host, sometimes subspherical, irregular and rough, often forming gall conglomerates, sometimes a single gall occupying the whole surface of the hymenium obscuring the thalline margin, (0.1)0.13–0.68(1.15) mm diam. (n = 80). Hyphae sometimes with clamp connections, thin-walled, up to 3 μm diam.; haustorial branches present, tremelloid, mother cell (2)2.5–4.1(5) μm diam. (n = 34), filament up to 7 μm in length. Hymenium reduced when young but developed when old, containing numerous broadly fusiform to ellipsoid probasidia with a basal clamp connection. Basidia subspherical to ellipsoid or pyriform, 2-celled when mature, with one transverse, oblique, or longitudinal septum, when transversely septate, sometimes constricted at the septa, when longitudinally septate, rarely cells elongating and growing separately, (10.5)13.6–31.8(39) × (7)8.4–15.0(23) μm (n = 140) [transversely septate: (13)18.0–31.8(39) × (7.5)9.7–14.2(18) μm (n = 38); obliquely septate: (10.5)14.8–27.4(36) × (7)8.9–15.0(21) μm (n = 62); longitudinally septate: (11)13.6–20.0(24.5) × (8.5)8.4–16.3(23) μm (n = 40)]; epibasidia elongate, (2.5)2.9–5.7(10.5) μm diam. (n = 68), up to at least 40 μm in length. Basidiospores subspherical, apiculus present, 5.5 × 6.0 μm (n = 1).

Etymology

From Rusavskia elegans, the host lichen.

Ecology and distribution

Tremella elegantis is known to grow only in the hymenium of Rusavskia elegans. The species is known from Norway and Sweden.

Notes

Tremella elegantis resembles T. caloplacae s. str. since it induces the formation of convex galls in the hymenium of its host. Tremella elegantis, however, grows exclusively on Rusavskia elegans and also differs from other species in the T. caloplacae complex in the size of the basidiomata (often > 1 mm diam.), the higher frequency of hyphae with clamp connections, the ellipsoidal to broadly fusiform probasidia, and the formation of basidia with cells elongating and growing separately when they are longitudinally septate. Both T. elegantis and T. sorediatae sometimes produce basidia with longitudinal septa where the cells grow separately, but basidia are smaller in T. elegantis. Species also showing basidia with these characteristics are T. christiansenii Diederich, T. diederichiana Pérez-Ort. et al., T. hypocenomycis Diederich, T. mayrhoferi J.C. Zamora et al. and T. tuckerae Diederich, but these differ in the larger (T. christiansenii, T. diederichiana, T. mayrhoferi and T. tuckerae) or smaller (T. hypocenomycis) basidia, and in that basidia can be 2–4-celled except for T. tuckerae (also 2-celled). The new species T. elegantis is phylogenetically homogeneous and is sister to T. sorediatae.

Additional specimens examined (all on Rusavskia elegans).

Norway: Finnmark: Vardø, Bukkemoltangen, Dolomites area, 70°25ʹ33ʺN, 30°45ʹ19ʺE, 25 m, 2014, Millanes 1085 (S). Oppland: Lom, Runningsgrende, Kleive, 61°42ʹ57ʺN, 8°14ʹ03ʺE, 750 m, 2013, Millanes 808 (S).—Sweden: Ångermanland: Grundsunda sn, Skagsudden, 2550 m S om Skags kapell, Skagsudde, 250 m WSW om fyren, 63°11ʹ12ʺN, 19°01ʹ11ʺE, 2 m, 2013, Odelvik, Hedenäs & Rönblom 14-453 (S). Torne Lappmark: Jukkasjärvi, Mt Paddos, 68°19ʹ8ʺN, 18°51ʹ54ʺE, 596 m, at the base of a cliff, 2013, Millanes 908 (S); Jukkasjärvi, Mt Paddos, 68°19ʹ10ʺN, 18°51ʹ56ʺE, 625 m, 2013, Millanes 904 (S).

Tremella nimisiana Freire-Rallo, Diederich, Millanes & Wedin sp. nov.

MycoBank No.: MB 847664

Differs from Tremella caloplacae in the size of the basidiomata (< 1 mm diam.), the higher frequency of hyphae with clamp connections, larger basidiospores (7.5–10.3 × 6.9–10.1 μm), and in developing only on Xanthocarpia spp.

Type: Spain, Guadalajara, Tendilla, Páramos de la Alcarria Occidental, 40°31ʹ44ʺN, 2°58ʹ60ʺW, 910 m, on calcareous rock, on Xanthocarpia marmorata, 2017, Millanes 1365 & Freire-Rallo (S—holotype). DNA voucher: SF291; GenBank Accession no: OQ192964 (ITS).

(Fig. 4)

Figure 4. Tremella nimisiana (A, E, M & S, holotype on Xanthocarpia marmorata; B, H, I, J, L, N–Q, B. de Lesdain 1906 on Xanthocarpia sp.; C, F, G, R & U, Hafellner 24839 on X. lactea; K & T, Thor 8202 on X. ferrarii). A–C, variation in gall morphology. D–G, I & J, 2-celled transversely septate basidia with haustoria and clamp connections. H, transversely septate 3-celled basidium. K & L, obliquely septate basidia. M & N, longitudinally septate basidia. O, hypha with clamp connection. P & Q, haustoria. R–U, basidiospores. Scales: A–C = 1 mm; D–N = 10 μm; O–U = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, yellowish orange to dark brown galls in the hymenium of the host, sometimes hemispherical, irregular and rough, sometimes smooth, often forming gall conglomerates, sometimes a single gall occupying the whole surface of the hymenium, (0.08–)0.07–0.30(–0.66) mm diam. Hyphae sometimes with clamp connections, thin-walled, up to 3 μm diam.; haustorial branches present, tremelloid, rarely with a bifurcated filament, mother cell rarely triangular, (2.5–)2.7–5.2(–7) μm diam. (n = 74), filament up to 17 μm in length. Hymenium reduced when young but developed when old, containing numerous broadly fusiform to ellipsoid probasidia with a basal clamp connection. Basidia narrowly elongate ellipsoid to pyriform, 2-celled when mature, with one transverse, rarely oblique or longitudinal septum, when transversely septate often stalked, rarely constricted at the septa, exceptionally 3-celled, with 2 transverse septa, clavate to subcylindrical, resembling Biatoropsis basidia, (17–)17.1–37.9(–55.5) × (7–)9.6–13.6(–17) μm (n = 142) [transversely septate: (17–)23.8–37.9(–55.5) × (7–)9.6–13.4(–17) μm (n = 132); obliquely septate: (18–)17.1–35.2(–48) × (11–)10.6–13.6(–15) μm (n = 8); longitudinally septate: (21.5–)21.0–23.6(–23.5) × (8–)6.9–11.9(–11.5) μm (n = 2)]; epibasidia elongate, (2.5–)2.9–5.7(–11.5) μm diam. (n = 62), up to at least 40 μm in length. Basidiospores subspherical to ellipsoid, apiculus present, (7–)7.5–10.3(–12) × (6–)6.9–10.1(–11.5) μm (n = 38).

Etymology

Named after Pier Luigi Nimis, Italian lichenologist, in recognition of his great work and contribution to lichenology.

Ecology and distribution

Tremella nimisiana is known to grow in the hymenium of Xanthocarpia ferrarii (Bagl.) Frödén et al., X. lactea, X. marmorata (Bagl.) Frödén et al. and Xanthocarpia sp. The species is known from Austria, Estonia, France and Spain.

Notes

Tremella nimisiana resembles T. caloplacae s. str. since it induces the formation of convex galls in the hymenium of its host. Tremella nimisiana, however, grows exclusively on Xanthocarpia spp. and also differs from other species in the T. caloplacae complex by the size of the basidiomata (often < 1 mm diam.), the higher frequency of hyphae with clamp connections, and the formation of 2-celled ellipsoid to pyriform basidia, or rarely 3-celled clavate to subcylindrical basidia. Other species within the T. caloplacae complex with occasionally 3-celled basidia are T. parietinae, T. pusillae and Tremella sp. 13, but these can be distinguished from T. nimisiana by their shorter and wider basidia. Another species commonly producing 3-celled basidia is Tremella phaeographinae Diederich & Aptroot, but this differs in the smaller basidia. The genetic differences among the specimens of T. nimisiana suggest that it is a potential species complex, which will probably be confirmed when there is a better knowledge of the species. The circumscription of Tremella nimisiana s. str. may therefore need to be modified in the future.

Additional specimens examined

Austria: Burgenland: Mühlgraben SW von Jennersdorf, bei den Gehöften, am Bachufer, 310 m, auf Beton einer alten Brücke, on Xanthocarpia lactea, 1990, Hafellner 24839 (GZU).—Estonia: Harjumaa: Tallinn Botanic Garden, Kloostiimetsa, 59°28ʹN, 24°52ʹE, 24 m, on X. ferrarii and Xanthocarpia sp., 1989, Thor 8202 (S).—France: Nord: Bray-Dunes à la frontière belge, sur les vieilles coquilles, on Xanthocarpia sp., 1906, B. de Lesdain (ANGUC—holotype of Caloplaca lactea f. ostreaeseda (Harm.) Zahlbr.) (Navarro-Rosinés & Hladun 1996).—Spain: Zaragoza: Belchite, La Lomaza de Belchite, road to Nª Sª del Rosario, 625 m, calcareous knoll, on X. marmorata, 2003, Etayo 20387 (hb. Etayo).

Tremella parietinae Freire-Rallo, Diederich, Millanes & Wedin sp. nov.

MycoBank No.: MB 847665

Differs from Tremella caloplacae in the higher frequency of hyphae with clamp connections, the broadly fusiform probasidia, the rarely 3-celled basidia, bigger basidiospores (6.5–11.9 × 5.7–11.9 μm), and in developing only on Xanthoria parietina.

Type: Spain, Madrid, Villaviciosa de Odón, Área Recreativa El Sotillo, 40°22ʹ03ʺN, 3°56ʹ44ʺW, 580 m, on the bark of Fraxinus sp., on Xanthoria parietina, 2017, Millanes 1328 (S—holotype). DNA voucher: SF390; GenBank Accession no: OQ418450 (ITS).

(Fig. 5)

Figure 5. Tremella parietinae on Xanthoria parietina (A, D, E, K, T & U, Diederich 17385; B, F, J, L, P & S, holotype; C, H, I, N, O & R, Diederich 17740; G, M, Q & V, Obermayer 12148a). A–C, variation in gall morphology. D & E, 3-celled basidia and transversely septate 2-celled basidium. F–J, transversely septate basidia with haustoria and clamp connections. K–N, obliquely septate basidia with haustoria and clamp connections. O, P & R, longitudinally septate basidia. Q, hypha with clamp connection. S–V, basidiospores. Scales: A–C = 1 mm; D–R = 10 μm; S–V = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, yellow to orange galls in the hymenium of the host, often hemispherical, smooth, uniform and scattered all over the hymenium, sometimes irregular and forming conglomerates, (0.05–)0.10–0.42(–1.18) mm diam. (n = 330). Hyphae sometimes with clamp connections, thin-walled, up to 3 μm diam.; haustorial branches present, tremelloid, rarely with a bifurcated filament, mother cell (2–)3.0–5.3(–6.5) μm diam. (n = 116), filament up to 10 μm in length. Hymenium reduced when young but developed when old, containing numerous broadly fusiform to ellipsoidal probasidia with a basal clamp connection. Basidia subspherical, pyriform or ellipsoid, 2-celled when mature, with one transverse, sometimes oblique, rarely longitudinal septum, when transversely septate sometimes constricted at the septum, or upper part subglobose and wider than the lower part, rarely basidia 3-celled with two oblique septa or one transverse and another oblique septum, rarely with a distinct stalk, (11–)14.0–34.3(–47.5) × (5–)9.7–21.5(–22) μm (n = 408) [transversely septate: (12–)20.7–34.3(–47.5) × (5–)10.1–14.3(–18.5) μm (n = 315); obliquely septate: (15–)19.6–30.3(–40) × (7.5–)9.7–14.6(–20.5) μm (n = 84); longitudinally septate: (11–)14.0–21.2(–23) × (14–)16.7–21.5(–22) μm (n = 9)]; epibasidia elongate or cylindrical, (2–)2.9–5.1(–7.5) μm diam. (n = 136), up to at least 43.5 μm in length. Basidiospores subspherical, apiculus present, (4–)6.5–11.9(–14.5) × (3–)5.7–11.9(–14.5) μm (n = 46).

Etymology

From Xanthoria parietina, the host lichen.

Ecology and distribution

Tremella parietinae is known to grow only in the hymenium of Xanthoria parietina. The species is known from Austria, Luxembourg, Portugal, Slovenia, Spain and Sweden but probably has a broader distribution as it seems not to be rare where Xanthoria parietina is present.

Notes

Tremella parietinae resembles T. caloplacae s. str. since it induces the formation of convex galls in the hymenium of its host, but it grows exclusively on Xanthoria parietina and also differs from other species in the T. caloplacae complex by the size of the basidiomata (often > 1 mm diam.), the higher frequency of hyphae with clamp connections, the ellipsoidal to broadly fusiform probasidia, and the formation of 2-celled or rarely 3-celled basidia. Tremella occultixanthoriae is another species growing on X. parietina, but it grows on the lower surface of the thallus and produces 4-celled basidia with longitudinal septa devoid of epibasidia. Differences among T. nimisiana, T. parietinae, T. pusillae and Tremella sp. 13 are discussed in the notes of T. nimisiana. The new species T. parietinae is phylogenetically homogeneous.

Additional specimens examined (all on Xanthoria parietina)

Austria: Kärnten: Zentralalpen, 46°50ʹ05ʺN, 14°47ʹ10ʺE, 550 m, 2010, Hafellner 77065 (GZU). Steiermark: Nordalpen, Dachstein-Gruppe, Ramsau, 47°25ʹ16ʺN, 13°38ʹ10ʺE, 1170 m, 2011, Obermayer 12148a (GZU); ibid., 2012, Obermayer 12446 (GZU); ibid., 47°25ʹ35ʺN, 13°39ʹ10ʺE, 1180 m, 2011, Obermayer 12147 (GZU); Oststeirisches Hügelland, Graz, Andritz, Pfanghofweg 40a, 47°06ʹ57ʺN, 15°26ʹ18ʺE, 410 m, 2011, Pinter 11010 (GZU); Oststeirisches Hügelland, Graz, Ragnitztal, 47°4ʹ35ʺN, 15°28ʹ50ʺE, 380 m, 2010, Hafellner 77075 (GZU).—Luxembourg: Pétange, Fuussbësch, 2012, Diederich 17385 (BR); Belvaux, Metzerbierg, 2012, Diederich 17455 (BR); Belvaux, Kiemreech, 2012, Diederich 17473 (BR); Strassen, Tossebierg, 2014, Diederich 17740 (BR).—Portugal: Lisboa: Monsanto Natural Park, 38°43ʹ44ʺN, 9°10ʹ54ʺW, 180 m, 2019, Etayo 31826 (hb. Etayo).—Slovenia: Southern Alps, Julian Alps, Cezsoča S of Bovec SE above the village, 46°19ʹ10ʺN, 13°33ʹ20ʺE, 380 m, 2003, Hafellner 77507 (GZU).—Spain: Castilla y León: Burgos, Santo Domingo de Silos, 41°57ʹ30ʺN, 3°24ʹ00ʺW, 1130 m, 2019, Etayo 31851 (hb. Etayo); Burgos, between Santo Domingo de Silos and Espinosa de Cervera, 41°54ʹ16ʺN, 3°28ʹ04ʺW, 1145 m, 2019, Etayo 31889 (hb. Etayo); Burgos, road from Lerma to Santo Domingo de Silos, 2019, Etayo 31970 (hb. Etayo); Segovia, San Ildefonso, 40°52ʹ22ʺN, 4°01ʹ07ʺW, 1220 m, 2010, Zamora, Zamora & Señoret 2010 (G). Extremadura: Cáceres, Monfragüe National Park, Villareal de San Carlos, 39°50.91ʹN, 6°02.48ʹW, 290 m, 2014, Millanes 1192 & Westberg (S); Cáceres, Monfragüe National Park, from Salto del Gitano to Fuente del Francés, 39°49ʹ42ʺN, 6°03ʹ02ʺW, 320 m, 2014, Millanes 1197 & Westberg (S). Madrid: El Escorial, 2011, Vivas, Zamora & Zamora (G); Pinilla, 40°55ʹ42ʺN, 3°48ʹ57ʺW, 1100 m, 2014, Millanes 1190 (S); same locality as the type, 2017, Millanes 1297, 1304, 1364 (S); 2019, Freire-Rallo S128 & Millanes (S); ibid., 2011, Zamora (BR).—Sweden: Östergötland: Nässja Parish, 58°27ʹ53ʺN, 14°48ʹ47ʺE, 109 m, 2013, Millanes 833, 849 (S).

Tremella pusillae Freire-Rallo, Diederich, Millanes & Wedin sp. nov.

MycoBank No.: MB 847666

Differs from Tremella caloplacae in the presence of ellipsoid probasidia, the rare presence of 3-celled basidia, the size of the basidiospores (7.6–9.2 × 6.7–10.2 μm), and in developing only on Calogaya pusilla.

Type: Sweden, Öland, Jordhamn, 57°05ʹ53ʺN, 16°53ʹ13ʺE, 6 m, on calcareous rock, on Calogaya pusilla, 2017, Freire-Rallo S33 (S—holotype). DNA voucher: SF234; GenBank Accession nos: OQ192934 (ITS), OQ176384 (LSU).

(Fig. 6)

Figure 6. Tremella pusillae on Calogaya pusilla (A, F, G, I, J, L, P–S, holotype; B, D, E, N, O, T, U & W, Freire-Rallo S37; C, K & M, Freire-Rallo S44; H & V, Freire-Rallo S45). A–C, variation in gall morphology. D–J, 2-celled transversely septate basidia. K–O, obliquely septate basidia. P, longitudinally septate basidium. Q–S, haustoria. F, T–W, basidiospores. Scales: A–C = 1 mm; D–P, T–W = 10 μm; Q–S = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, light orange to brown galls in the hymenium of the host, hemispherical, irregular and rough, rarely smooth and uniform, often forming gall conglomerates in the hymenium of the host, sometimes the thalline margin of the host is not visible, (0.13–)0.14–0.55(–1.5) mm diam. (n = 84). Hyphae thin-walled, up to 3 μm diam., clamp connections not observed; haustoria rarely observed, haustorial branches tremelloid, mother cell (2.5–)2.3–4.8(–5) μm diam. (n = 3), filament up to 4 μm in length. Hymenium reduced when young but developed when old, containing numerous ellipsoid probasidia. Basidia ellipsoid or pyriform, 2-celled when mature, rarely 3-celled, often with one transverse or oblique, rarely longitudinal septum, when transversely septate, sometimes constricted at the septum, (13–)15.6–26.7(–30) × (6.5–)9.5–19.3(–18.5) μm (n = 58) [transversely septate: (13–)18.6–26.7(–30) × (6.5–)9.5–13.0(–15.5) μm (n = 38); obliquely septate: (13.5–)19.2–26.2(–28) × (9–)9.6–14.4(–18.5) μm (n = 18); longitudinally septate: (17–)15.6–23.3(–22.5) × (15–)14.2–19.3(–18.5) μm (n = 2)]; epibasidia cylindrical to elongate, (2.5–)2.9–5.2(–6) μm diam. (n = 16), up to at least 34 μm in length. Basidiospores subspherical, apiculus present, (7–)7.6–9.2(–9.5) × (7–)6.7–10.2(–11) μm (n = 10).

Etymology

From Calogaya pusilla, the host lichen.

Ecology and distribution

Tremella pusillae induces galls in the hymenium of Calogaya pusilla. It is known only from Sweden.

Notes

Tremella pusillae resembles T. caloplacae s. str. since it induces the formation of convex galls in the hymenium of its host. Tremella pusillae, however, grows exclusively on Calogaya pusilla and also differs from other species in the T. caloplacae complex by the size of the basidiomata (often > 1 mm diam.), the absence of hyphae with clamp connections, the subspherical to ellipsoidal probasidia, and the formation of 2-celled or rarely 3-celled basidia. Differences among T. nimisiana, T. parietinae, T. pusillae and Tremella sp. 13 are discussed in the notes of T. nimisiana. The new species T. pusillae is phylogenetically homogeneous and is closely related to Tremella sp. 13.

Additional specimens examined (all in Calogaya pusilla)

Sweden: same locality as the type, 2017, Freire-Rallo S34, S44, S45 (S). Östergötland: Nässja parish, 58°27ʹ53ʺN, 14°48ʹ47ʺE, 112 m, on calcareous rocks on the church wall, 2013, Millanes 835 (S).

Tremella sorediatae Freire-Rallo, Diederich, Millanes & Wedin sp. nov.

MycoBank No.: MB 847667

Differs from Tremella caloplacae and from other species in the T. caloplacae complex in the development of basidiomatal galls on the host thallus instead of the hymenium, and in the presence of basidia with longitudinal septa with cells elongating and growing separately.

Type: Greenland, Qagssiarsuk, open area, 61°10ʹN, 45°35ʹW, on rock, on Rusavskia sorediata, 2005, Kukwa 4385a (UGDA—holotype; BR, S—isotypes). DNA voucher: AM32; GenBank Accession nos: OQ192945 (ITS), OQ176393 (LSU).

(Fig. 7)

Figure 7. Tremella sorediatae on Rusavskia sorediata (A, C, F, G, J, K, L, P, Q, S & T, holotype; B, D, E, H, I, M, N, O & R, Goward 01-608). A–C, morphological variation in gall morphology. D–F, 2-celled transversely septate basidia. G–J, obliquely septate basidia. K–O, longitudinally septate basidia. P, probasidium with haustorium and clamp connection. Q–T, basidiospores. Scales: A–C = 1 mm; D–P = 10 μm; Q–T = 5 μm. In colour online.

Basidiomata growing on the host thallus, inducing the formation of convex, orange to brown galls, more or less subspherical, irregular and rough, often forming gall conglomerates, (0.19–)0.15–0.66(–1.34) mm diam. (n = 29). Hyphae thin-walled, up to 3 μm diam., clamp connections not observed; haustorial branches present, tremelloid, mother cell (2–)2.2–3.9(–4.5) μm diam. (n = 21), filament up to 7 μm in length. Hymenium reduced when young but developed when old, containing numerous ellipsoid probasidia with a basal clamp connection. Basidia ellipsoid, pyriform, 2-celled when mature, often with one transverse or oblique, rarely longitudinal septum, when transversely septate, sometimes constricted at the septum, when longitudinally septate, sometimes cells elongating and growing separately, (12–)15.0–22.6(–24.5) × (7.5–)8.7–16.2(–16) μm (n = 42) [transversely septate: (12–)16.5–22.6(–24.5) × (7.5–)8.7–12.7(–14.5) μm (n = 18); obliquely septate: (12.5–)15.0–21.3(–24.5) × (8–)8.8–13.0(–15) μm (n = 20); longitudinally septate: (16–)16.7–19.3(–19) × (13–)13.2–16.2(–16) μm (n = 4)]; epibasidia elongate, (2–)2.1–4.1(–4) μm diam. (n = 20), up to at least 25 μm in length. Sterigma not observed. Basidiospores subspherical to ellipsoid, apiculus present, (4–)4.1–5.7(–6) × (3–)3.0–4.5(–5) μm (n = 8).

Etymology

From Rusavskia sorediata, the host lichen.

Ecology and distribution

Tremella sorediatae induces galls on the thallus of Rusavskia sorediata. The species is known from Greenland and Canada.

Notes

Tremella sorediatae grows exclusively on Rusavskia sorediata and differs from other species in the T. caloplacae complex by being the only species that induces galls on the thallus of its host. It is similar to T. xanthomendozae, a species apparently confined to Xanthomendoza weberi, that induces the formation of galls on the thallus of its host, but differs in the smaller size of its basidia and basidiospores. Differences with T. elegantis are discussed in the notes of this species. We have studied only two specimens of T. sorediatae and they form a supported monophyletic lineage. However, the genetic differences between the two samples suggest that further material and studies are needed to clarify whether this is a single species or a species complex.

Additional specimen examined

Canada: British Columbia: Crown Lake, Marble Canyon Provincial Park, 25 km NE of Lillooet, 600 m, on Rusavskia sorediata, 2001, Goward 01-168 (BR, UBC).

Tremella sp. 13 (on Calogaya biatorina)

(Fig. 8)

Figure 8. Tremella sp. 13 on Calogaya biatorina (Etayo 20762). A–C, variation in gall morphology. D, 3-celled basidium. E–J, L & M, 2-celled transversely septate basidia with haustoria and clamp connections. N & O, obliquely septate basidia. K, P–R, longitudinally septate basidia. S & T, haustoria. U–X, basidiospores. Scales: A–C = 1 mm; D–R = 10 μm; S–X = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, light to dark orange galls in the hymenium of the host, hemispherical, smooth and uniform, often several galls on the same apothecium but not forming aggregates, (0.12–)0.17–0.35(–0.48) mm diam. (n = 35). Hyphae thin-walled, up to 3 μm diam., clamp connections not observed; haustoria rarely observed, haustorial branches tremelloid, mother cell (3.5–)3.6–5.5(–6) μm diam. (n = 11), filament up to 5 μm in length. Hymenium reduced when young but developed when old, containing numerous broadly fusiform to ellipsoid probasidia. Basidia narrowly elongate ellipsoid to subspherical, pyriform, 2-celled when mature, rarely 3-celled, often with one transverse septum, rarely with oblique or longitudinal septum, when transversely septate, sometimes constricted at the septum, (19–)20.0–33.3(–41.5) × (10.5–)11.4–16.8(–17) μm (n = 47) [transversely septate: (19–)24.2–33.3(–41.5) × (10.5–)11.4–14.5(–17.5) μm (n = 38); obliquely septate: (23.5–)24.0–31.2(–33.5) × (12.5–)12.6–16.2(–17) μm (n = 6); longitudinally septate: (20–)20.0–21.4(–21.5) × (14.5–)14.6–16.8(–17) μm (n = 3)]; epibasidia elongate, (3.5–)4.1–5.8(–7) μm diam. (n = 29), up to at least 61 μm in length. Basidiospores subspherical, apiculus present, (8.5–)8.7–10.2(–10.5) × (8–)8.2–10.3(–10.5) μm (n = 5).

Ecology and distribution

Tremella sp. 13 induces galls in the hymenium of Calogaya biatorina. It is known only from Spain.

Specimen examined

Spain: Huesca: ascent slope to Góriz, 1990 m, on Calogaya biatorina, 2003, Etayo 20762 (hb. Etayo).

Tremella sp. 14 (on Calogaya decipiens)

(Fig. 9)

Figure 9. Tremella sp. 14 on Calogaya decipiens (Millanes 850). A–C, variation in gall morphology. D–K, 2-celled transversely septate basidia with haustoria and clamp connections. L & M, obliquely septate basidia. N, longitudinally septate basidium. O, haustorium. P, basidiospore. Scales: A–C = 1 mm; D–N = 10 μm; O & P = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, dark yellow to light brown galls in the hymenium of the host, subspherical, irregular, (0.09–)0.08–0.39(–0.81) mm diam. (n = 23). Hyphae up to 3 μm diam., clamp connections not observed; haustoria rarely observed, haustorial branches tremelloid, mother cell (2–)2.0–4.1(–4) μm diam. (n = 2), filament up to 3 μm in length. Hymenium reduced when young but developed when old, containing numerous ellipsoid probasidia. Basidia ellipsoid to subspherical, 2-celled when mature, with one transverse septum, rarely obliquely or longitudinally septate, when transversely septate, sometimes upper part subglobose and wider than the lower part, (11–)13.2–19.4(–23) × (8–)8.3–11.4(–14.5) μm (n = 39) [transversely septate: (11–)13.2–18.9(–23) × (8–)8.4–11.1(–14.5) μm (n = 33); obliquely septate: (16.5–)16.0–19.4(–20) × (8.5–)8.3–10.4(–10.5) μm (n = 4); longitudinally septate: (14–)13.7–16.9(–16.5) × (9–)8.8–11.4(–11) μm (n = 2)]; epibasidia elongate, (2–)2.4–3.2(–3.5) μm diam. (n = 16), up to at least 24 μm in length. Basidiospores subspherical, apiculus present, 5.5 × 4.5 μm (n = 1).

Ecology and distribution

Tremella sp. 14 induces galls in the hymenium of Calogaya decipiens. It is known only from Sweden.

Specimen examined

Sweden: Östergötland: Nässja parish, historically interesting area with an ancient stone circle, a churchyard, and a church, 58°27ʹ53ʺN, 14°48ʹ47ʺE, 109 m, on Calogaya decipiens, 2013, Millanes 850 (S).

Tremella sp. 15 (on Polycauliona)

(Fig. 10)

Figure 10. Tremella sp. 15 on Polycauliona sp. (Etayo 19125). A–C, variation in gall morphology. D–I, 2-celled transversely septate basidia with haustoria and clamp connections. K–N, obliquely septate basidia with haustoria and clamp connections. J, probasidia with haustorium. O, hypha with clamp connection. P, basidiospore. Scales: A–C = 1 mm; D–N = 10 μm; O & P = 5 μm. In colour online.

Basidiomata reduced, inducing the formation of convex, dark orange galls in the hymenium of the host, hemispherical, smooth and uniform, sometimes irregular, scattered all over the hymenium but sometimes forming gall conglomerates, (0.07–)0.08–0.25(–0.82) mm diam. (n = 18). Hyphae sometimes with clamp connections, up to 3 μm diam.; haustoria rarely observed, haustorial branches tremelloid, rarely with two filaments or one bifurcated filament, mother cell (2–)2.6–4.7(–5.5) μm diam. (n = 13), filament up to 7.0 μm in length. Hymenium reduced when young but developed when old, containing numerous broadly fusiform to ellipsoid, pyriform probasidia. Basidia narrowly elongate ellipsoid to ellipsoid, 2-celled when mature, with one transverse septum, rarely obliquely septate, when transversely septate, sometimes stalked, sometimes laterally elongated cells resembling Biatoropsis basidia, (20.5–)26.5–40.5(–52) × (8–)10.5–13.6(–15) μm (n = 54) [transversely septate: (20.5–)26.5–40.5(52) × (8–)10.5–13.6(–15) μm (n = 53); obliquely septate: 25.5 × 13.5 μm (n = 1)]; epibasidia elongate, (2.5–)3.3–4.9(–5) μm diam. (n = 19), up to at least 37 μm in length. Basidiospores subspherical, apiculus present, 6.5 × 7.0 μm (n = 1).

Ecology and distribution

Tremella sp. 15 induces galls in the hymenium of Polycauliona sp. It is known only from Spain.

Specimen examined

Spain: Teruel: between Rubielos and Mora, Fuentes del Ocino, 1100 m, on Polycauliona sp., 2002, Etayo 19125 (hb. Etayo).