Introduction
More than 1800 lichenicolous species of fungi are known which live on lichens as host-specific parasites, pathogens, saprotrophs and commensals (Lawrey & Diederich Reference Lawrey and Diederich2003). The genus Arthonia (Arthoniaceae, Arthoniales) accommodates c.500 species worldwide (Grube Reference Grube, Nash, Ryan, Diederich, Gries and Bungartz2004). Out of these, c. 110 ascomycetes are described from different facultative lichenicolous fungi (Lawrey & Diederich Reference Lawrey and Diederich2011). Lichen-inhabiting fungi in the Indian subcontinent are little studied, perhaps due to a lack of knowledge of their substratum specificity. Some examples reported from Nepal and India are: Arthonia destruens var. nana Grube & Hafellner reported from central Himalaya (Nepal), inhabiting Xanthoria fallax (Hepp) Arnold (Grube et al. Reference Grube, Matzer and Hafellner1995); Polysporina lapponica (Ach. ex Schaer.) Degel. [=P. dubia (H. Magn.) Vězda] from the western and north-west Himalayas (India), growing on Acarospora (Awasthi Reference Awasthi1991); and Lichenopeltella swaminathaniana Hariharan et al. from the Eastern Ghats (India) on Porina species (Hariharan et al. Reference Hariharan, Mibey and Hawksworth1996). During ongoing research into lichenicolous, lichenized and non-lichenized fungi of the tropical and sub-tropical regions in India, several noteworthy samples of lichens were collected and preserved. A re-examination of herbarium specimens resulted in the identification of an interesting Arthonia species growing luxuriantly on Diorygma junghuhnii. The species A. diorygmae is recognized as a lichenicolous fungus and described here as new to science.
Material and Methods
Specimens of lichens preserved in the herbarium of the CSIR-National Botanical Research Institute, Lucknow (LWG), were studied. Morphological and anatomical characters were examined using stereozoom (LECIA S8AP0) and compound (LECIA DM500) microscopes, respectively. The colour tests and thin-layer chromatography in solvent system A were performed following Orange et al. (Reference Orange, James and White2001). Lugol's solution (I) was used to check the amyloidity in asci, interascal filaments and ascospores.
The New Species
Arthonia diorygmae S. Joshi & Upreti sp. nov.
MycoBank No.: MB802979
Arthonia diorygmae is differentiated from other 1-septate, lichenicolous Arthonia species in having immersed, finally flattened to ± convex, roundish to irregular ascomata, a slightly whitish pruinose disc, densely inspersed interascal filaments, large asci (40–57×10–18 µm), ascospores (13–)14–15(–21)×5–7 µm and Diorygma junghuhnii as host species.
Type: India, Palni Hills, Perumalmalai area, on bark, 5 January 1970, D. D. Awasthi & K. P. Singh 70.425 (LWG—holotype).
Fig. 1. Arthonia diorygmae. A, habit & habitat (holotype); B, cross-section of ascomata; C & D, ascus with ascospores; E, colourless ascospores; F, ascospores at maturity. Scales: A=1 mm; B=100 µm; C & E=20 µm; D & F=15 µm. In colour online.
Ascomata apothecia, arthonioid, scattered to crowded, ± evenly distributed, scarcely confluent in groups of two, at first immersed later erumpent, appearing level with the thallus in older ascomata, applanate to ± convex, roundish to irregular in shape, up to 0·3 mm diam., in section they exhibit an undulating V-shaped structure, up to 160 µm tall. Disc dark brown, gelatinous, slightly whitish pruinose, 0·10–0·25 mm diam. Epithecioid layer hyaline to brownish to olivaceous (5–) 10–15(–20) µm high, continuous with the parathecioid layer, K+ slightly purplish, I+ wine red, KI+ wine red. Parathecioid layer brown to dark brown or olivaceous, (10–) 15–20(–30) µm thick; ascigerous layer hyaline, (45–)60–70 µm high. Interascal filaments paraphysoidal, anastomosingly branched, 1–2 µm thick, densely conglutinate and inspersed, apically swollen and branched, hymenial gel between the filaments I+ blue, KI+ blue to wine red. Hypothecioid layer hyaline to reddish brown later, 20–30(–40) µm high, I+ wine red, KI+ wine red. Asci clavate, 8-spored, stiped, outer wall I+ blue, KI−, epiplasm I+ wine red, KI+ wine red, 40–57×10–18 µm. Ascospores hyaline, becoming smoky to greyish at maturity, transversely 1-septate (2-celled), ovoid to slipper-shaped, constricted at the septum, the upper cell slightly thicker than lower, perispore distinct, up to 1 µm thick, I−, KI−, (13–)14–15(–21)×5–7 µm.
Chemistry
Apothecia (A. diorygmae): K−, PD−, C−. Thallus (host species): K+ yellowish red, PD+ yellow, C−; norstictic acid detected by TLC.
Etymology
The species name refers to the host lichen genus Diorygma.
Ecology and distribution
Arthonia diorygmae is reported from the eastward spur of the Western Ghats in India. The species flourishes with other lichenized or non-lichenized fungi growing on the trees of tropical rainforests in the Perumalmalai hills of Tamil Nadu, at an altitude of 1320 m. The host lichen Diorygma junghuhnii grows in the evergreen (rain) forests of the Western Ghats, the eastern Himalayas and the Eastern Ghats in India. Recent collections confirm the expanded distribution of the host species to the north-west Himalayas. Hence, Arthonia diorygmae may also have a wider distribution in India.
Remarks
No lichenicolous fungi have ever been described from Diorgyma. However, a few have been recorded from other species in the family Graphidaceae. Arthonia diorygmae shows a parasitic life form on Diorygma junghuhnii (Graphidaceae), spreading over the host thallus and restricting the development of ascocarps. The species is distinguished from other species of lichenicolous Arthonia with 1-septate spores by its unique habitat on Diorygma junghuhnii, immersed to ± erumpent ascomata up to 160 µm high in cross-section, dark brown, mostly irregular, slightly whitish pruinose discs, an undulating brown parathecioid layer, a K+ purplish epithecioid layer, an ascigerous layer up to 70 µm high, asci 40–57×10–18 µm, slipper-shaped and hyaline, smoky to dark greyish ascospores of (13–)14–15(–21)×5–7 µm.
Almost all 1-septate Arthonia share a similar range of apothecial and ascospore size. The new taxon most closely resembles Arthonia amylospora Almq., which has an ± applanate ascomatal disc 0·10–0·35 mm diam., colourless ascospores 13–21×5–8 µm (16–24×6–10 µm) (Ihlen & Wedin Reference Ihlen and Wedin2008; Coppins & Aptroot Reference Coppins, Aptroot, Smith, Aptroot, Coppins, Fletcher, Gilbert, James and Wolseley2009) and lacks a visible vegetative thallus but differs in being commensalistic on Porpidia rugosa, in having mostly immersed ascomata gathered in small clusters, the lack of a K+ purplish pigment in the epithecioid layer, a pale brown ascigerous region (40–55 µm high) and K/I+ blue ascospores.
Arthonia peltigerea Th. Fr., A. semi-immersa Wedin & Hafellner, A. punctella Nyl., A. destruens Rabenh. and A. plectocarpoides (S. Y. Kondr. & D. J. Galloway) Wedin & S. Y. Kondr. also have similar ascospore sizes of 15–20×5–7 µm, c. 14·5–18·0×5–7 µm, 12–17×5·0–7·5 µm, 10·5–17·0×5–7 µm and 11–17×4·0–6·5 µm, respectively. Arthonia peltigerea is a weak parasite on the thallus of Peltigera rufescens, has somewhat hemispherical ascomata 0·3–1·5 mm diam. and a pale brown, 45–50 µm tall, ascigerous layer. Arthonia semi-immersa Wedin & Hafellner, although having a similar hymenium size (60–70 µm), hyaline ascospores and a parasitic mode of action similar to that of A. diorygmae, has an entirely different lecideoid ascomatal origin, with immersed to superficial (after rupturing the host cortex) ascomata arranged in a row of 3–5 in a fissured cortex and with ascospores lacking a perispore. Arthonia punctella is most probably an endemic species to the British Isles, with slightly smaller ascomata, 0·07–0·20 mm diam., ascospores which soon become brown and warty, and is commensalistic on the thallus of Diplotomma. Arthonia destruens Rabenh., a local parasite on Physcia stellaria and Xanthoria parietina, has ascomata ± crowded in groups of 10, a yellowish hymenium containing an amorphous pigment and 4–8-spored asci. Arthonia plectocarpoides has a hypothecioid layer, 45–55 µm high, and is distinctly cecidogenous (gall forming) on Pseudocyphellaria scabrosa and alpine species of Heterodermia. All the above species, except Arthonia destruens, lack a K+ purplish epithecioid layer. Other similar Arthonia species, with a K+ purplish epithecioid layer, include A. cohabitans Coppins, A. neglectula Nyl., and A. destruens var. nana Grube & Hafellner. Arthonia cohabitans differs in lacking an epithecioid layer in mature ascomata, has an indistinct parathecioid layer, a yellowish brown ascigerous layer and lives on Arthothelium macounii. Arthonia neglectula has much smaller ascospores of 7–10×3–4 µm, and grows on the sterile sorediate crust of Lepraria. The sympatric Arthonia destruens var. nana Grube & Hafellner, with dispersed ascomata and a parathecioid layer formed by down-turning of epithecium, is similar to the new taxon but is clearly distinguished by having comparatively small, 0·09–0·17 mm diam. ascomata, a pigmented ascigerous layer, 4–8-spored asci with an indistinct foot, 10·5–13·0×5–7 µm ascospores and occurring on Xanthoria fallax.
The family Graphidaceae comprises a large group of tropical and subtropical species. In India the family is represented by c. 408 species (c. 24 of Diorygma), with the majority occurring in the rainforests of the north-east Himalayas and the Western Ghats. The wide distribution of different groups of Graphidaceae in wet conditions enhances the possibility of overgrowth by non-lichenized fungi. In addition to the new taxon described here from India, only two additional parasitic Arthonia species are known to occur on Graphidaceae: Arthonia graphidicola Coppins and A. thelotrematis Coppins. Arthonia graphidicola, on the thallus of Graphis scripta, shows a resemblance to the new species in having colourless ascospores of similar dimensions (13–17×4·5–5·5 µm). It has earlier been recorded from the British Isles as endemic, but also occurs in France, Spain and Luxembourg (Coppins Reference Coppins1989; Coste Reference Coste1993, Reference Coste1997; Etayo & Diederich Reference Etayo and Diederich1998). It is very different because of the smaller apothecia which are 0·06–0·16 mm in diam. or elongate, fleck-like with pointed ends, up to 0·42×0·06–0·10 mm, with a pale reddish brown ascigerous layer (40–50 µm high) and 2–3-septate ascospores. Similarly, A. thelotrematis reported by Coppins (Reference Coppins1989) also differs from A. diorygmae in having the same apothecial morphology and ascospore septation as that of A. graphidicola, in addition to a comparatively smaller ascigerous layer (33–35 µm high) and ascospores (11–14×4·5–5·0 µm), and parasitic being on the thallus of Thelotrema lepadinum.
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1 Ascospores 1-septate, ascomata up to 0·3 mm, slightly pruinose, spores hyaline to greyish in late maturity; growing on Diorygma junghuhnii ... A. diorygmae
Ascospores 2–3-septate, ascomata epruinose, ascospores brown-warty at maturity; host lichen different ... 2
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2(1) Ascospores 13–17×4·5–5·5 µm, ascomata 0·06–0·16 mm diam.; hypothecium colourless; growing on Graphis scripta ... A. graphidicola
Ascospores 11–14×4·5–5·0 µm, ascomata 0·06–0·20 mm diam.; hypothecium reddish brown; growing on Thelotrema lepadinum ... A. thelotrematis
Key to Arthonia species growing on Graphidaceae
We are grateful to the Director of the National Botanical Research Institute (CSIR-NBRI), Lucknow, for providing laboratory facilities and the Ministry of Environment and Forests, New Delhi, for financial assistance. Santosh Joshi thanks Dr Alan W. Archer for valuable comments and suggestions, and Roshni Khare for help.
