Mixtura
Mixtura O.E. Erikss. & J.Z. Yue, Mycotaxon 38: 203 (1990).
Index Fungorum number: IF 25518; Facesoffungi number: FoF 00278, 1 morphological species (Species Fungorum 2022), molecular data unavailable.
Pathogen causing necrotic leaf spots on Chusquea serrulata. Lesions up to 2–5 cm long, infecting typically the leaf margin, elongate cylindrical, pale brown to yellowish brown, dry, separated from healthy tissue by a reddish-brown to purple-brown or black margin. Sexual morph: Ascomata scattered, sometimes clustered, solitary, immersed, visible as raised, small black dots on leaf lesions, uniloculate, globose to subglobose, glabrous, dark brown to black, ostiole central with minute papilla. Peridium thin-walled, of unequal thickness, thickened at apex at sides, composed of 3 or more layers of brown to dark brown, pseudoparenchymatous cells, arranged in a textura angularis, outer layers comprising 2–5 layers of thickened cells, brown to dark brown, inner layers comprising several layers of flattened cells, hyaline to pale brown. Hamathecium composed of numerous, 3–8 μm wide, filamentous, frequently anastomosing, broad cellular pseudoparaphyses, with distinct septa which are constricted at the septa, embedded in mucilaginous matrix. Asci 8-spored, bitunicate, fissitunicate, globose to subglobose, or ovoid, sessile to subsessile, apically rounded with well-developed ocular chamber, producing a few asci, arising from the basal ascoma. Ascospores irregular overlapping 4-seriate, phragmosporous, broadly fusiform with rounded, germ pore at the ends, initially hyaline to pale brown, becoming yellowish-brown or brown at maturity, paler at the end cells, distoseptate with 7-septa, slightly curved, rough, thick-walled, surrounded by thin, distinct sheath. Asexual morph: Unknown (adapted from Phookamsak et al. 2014).
Type species: Mixtura saginata (Syd.) O.E. Erikss. & J.Z. Yue
Notes: Mixtura is characterised by globose to subglobose small black ascomata on leaf lesions, globose to subglobose, or ovoid, sessile to subsessile asci, and overlapping 4-seriate, phragmosporous, hyaline to pale brown ascospores. Mixtura resembles Mycosphaerella in having a pathogenic lifestyle but differs in the centrum type (Eriksson & Yue 1990, Zhang et al. 2012). Mixtura resembles Trematosphaeria in having subglobose to globose ascomata and ellipsoidal to fusiform ascospores but differs in that the ascospores of the latter genus are olive brown and asci are clavate to cylindrical (Zhou et al. 2014). Eriksson and Yue (1990) placed Mixtura in Phaeosphaeriaceae based on the peridium structure. Zhang et al. (2012) transferred Mixtura to Teratosphaeriaceae based on morphological similarity with the type species of Teratosphaeria. Mixtura resembles Hadrospora but differs in that the latter forms trabeculate pseudoparaphyses while Mixtura has broad cellular pseudoparaphyses, with distinct septa. Zhang et al. (2012) and Phookamsak et al. (2014) excluded Mixtura from Phaeosphaeriaceae based on phylogenetic analyses. Mixtura resembles Leptosphaerulina in having clavate or saccate 8-spored asci but differs in the ascospores and centrum type in that the latter lacks pseudoparaphyses and has muriform ascospores. Phookamsak et al. (2014) tentatively placed Mixtura in Didymellaceae. Mixtura is a distinct genus in Didymellaceae but this placement is doubtful and molecular data is needed for confirmation.
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