Synarthonia Müll.Arg. (Müller 1891: 85)

MycoBank number: MB 5329; Index Fungorum number: IF 5329; Facesoffungi number: FoF;

Type species: Synarthonia bicolor Müll.Arg. (= Synarthonia inconspicua).

Thallus corticolous, rarely absent when young or throughout the life cycle (non-lichenized lichenicolous fungus), crustose, endophloeodal to epiphloeodal, whitish to greenish-grey to green, with or without white striae or spots, continuous to cracked, smooth to verrucose or farinose, sorediate or esorediate, ecorticate; thallus hyphae hyaline. Prothallus not observed, or forming a black to brown compact line in contact with other lichens, sometimes fibrous-like (S. psoromica and S. stigmatidialis) or rhizomorph-like (S. sikkimensis). Photobiont trentepohlioid, in short chains or single-celled, the cells globose to ellipsoid, absent in the non-lichenized lichenicolous species. Ascomata solitary or forming irregular clusters in most of the species, immersed to slightly elevated above thallus level to ± sessile; disc white, greyish or orange pruinose (brown to orange when pruina removed), light brown and almost translucent or blackish-brown with remnants of thallus. Excipulum hyaline to pale brownish to straw-coloured, composed of brown pigmented or hyaline hyphae, non-carbonized. Epihymenium pale brownish, formed by branched and anastomosing brown-walled (K+ olivaceous or K-) or hyaline (K-), 1.3–2.3 µm wide paraphysoids with tips thickened or not, inspersed with hyaline, red-brown to orange granular crystals. Hymenium hyaline, not inspersed or rarely inspersed with hyaline or orange granular crystals, I+ directly red, I+ blue rapidly turning into red or I+ persistently blue, K/I+ blue. Paraphysoids hyaline, branched and anastomosing, ± parallel between the asci and forming a dense or loose mesh around the asci. Hypothecium hyaline, yellowish or brownish. Asci broadly clavate, obovoid to ellipsoid or (sub-)globose, 8-spored, with or without K/ I+ blue ring like structures in the tholus, occasionally with a distinct or indistinct ocular chamber. Ascospores persistently hyaline, or brownish and ornamented with small brown (K+ olivaceous) warts at late maturity, ellipsoid to oblong-ovoid, transversely septate with an enlarged apical cell or muriform, with or without a gelatinous sheath. Pycnidia black, walls brown. Conidia hyaline, bacilliform, non-septate, straight to slightly curved.

Chemistry – Parietin, evernic acid, psoromic acid, unidentified xanthones, unknown secondary compounds or secondary compounds absent. Calcium oxalate crystals absent in most of the species (occasionally present in the ascomata of S. muriformis).

Distribution and ecology – Lichenized species of Synarthonia occur mainly in the tropics, more rarely in temperate regions, and are corticolous with a preference for smooth barked trees and rather exposed conditions (branches, free standing trees). The (facultatively) lichenicolous species of the S. ochracea complex appear to be restricted to corticolous species of Graphis early in their development, while S. rimeliicola is living on species of Parmeliaceae.

Notes –The genus Synarthonia is characterized by a com- bination of the following characters: ascomata often aggregated in clusters, ascospores transversely septate with an enlarged apical cell or muriform, and a secondary chemistry including evernic acid, psoromic acid, xanthones, unknown secondary compounds, or compounds absent.

According to Joseph & Sinha (2015) the genus Synarthonia is characterized by solitary ascomata becoming mono- to pluri-carpocentral synascomata embedded in a slightly elevated to immersed pseudostroma, with a thin white thalline margin. Cross sections of ascomata in some of our specimens showed two or three loculi of hymenium separated by thin interhymenial strands suggesting synascomata (fig. 2C). However, these interhymenial strands may also be caused by ascoma branching or grouped ascomata and cannot be differentiated from excipular hyphae. Moreover, this character is not always easy to observe. Therefore, we decided not to use the terminology of Joseph & Sinha (2015) pending further studies on the ascoma ontogeny of Synarthonia.

According to Joseph & Sinha (2015), the asci in the genus Synarthonia belong to the Arthonia-type. This is one of the four main ascus types in Arthoniales (Grube 1998), characterized by an obovoid (clavate) shape in combination with a thin lateral ascus wall and a large apical dome pierced by a distinct ocular chamber. To our observations, the shape of the asci in Synarthonia is rather variable and varies between broadly clavate, obovoid to ellipsoid or (sub-)globose. A dis- tinct ocular chamber is only occasionally present in some of the species.