Alternariaster centaureae-diffusae R.H. Perera, Bulgakov, Ariyawansa & K.D. Hyde, sp. nov.

Index Fungorum number: IF 551462, Facesoffungi number: FoF 01155

Etymology: The specific epithet centaureae-diffusae is based on the host plant species from which the fungus was isolated.

Holotype: MFLU 15-1521

Saprobic on dead stems of Centaurea diffusa Lam. Sexual morph: Ascomata 170–360 μm high, 146–290 μmdiam., solitary or in groups of 2–10, erumpent through host tissue, semi-immersed or nearly superficial, uniloculate, globose to subglobose, coriaceous, black, ostiolate. Ostiole periphysate, papillate, black.Periphyses aseptate, wide, with a blunt apex, hyaline.Peridium 40–70 μm (x̄ = 50 μm, n = 10) wide, composed of 5–10 rows of scleroplectenchymatous cells, outer part thin, amorphous and black, central part widest, comprising thick-walled cells of textura globularis, inner layer composed of flattened cells of textura angularis. Hamathecium comprising 3–4 μm wide, dense, hyaline, distinctly septate, branched, cellular pseudoparaphyses, embedded in a gelatinous matrix. Asci 130–170×11–13 μm (x̄ = 150 × 12 μm, n = 20), 8-spored, bitunicate, fissitunicate, cylindrical to cylindric-subclavate, with a short bulbous pedicel, rounded at the apex. Ascospores 76–132 × 2.2–4 μm (x̄ = 104 × 3.2 μm, n = 40), fasciculate, filiform, multi-septate, constricted at the apical septum, apical cell swollen, conical, yellowishbrown, smooth-walled, with a mucilaginous cap. Asexual morph: undetermined.

Material examined: RUSSIA, Rostov region, Shakhty city, 20th anniversary of Red Army urban microdistrict, Solyonaya Balka hollow, steppe on stony slope, on dead stems of Centaurea diffusa Lam. (Asteraceae), 17 June 2014, T. Bulgakov RU-83 (MFLU 15-1521, holotype); ibid., (GZAAS, isotype); ex-type living cultures MFLUCC 14-0992, ICMP. RUSSIA, Rostov region, Oktyabrsky district, Persianovsky rural settlement, ruderal plant community on railroad embankment, on dead stems of Centaurea diffusa Lam., 04 June 2014, T. Bulgakov RU-111 (MFLU 15-0009, paratype), ex-type living culture MFLUCC 14-1158.

Fig. Alternariastercentaureae-diffusae(MFLU 15-1521) a, b Appearance of ascomata on host substrate.c. Vertical section through ascoma. d. Close-up of the peridium. e. Cellular pseudoparaphyses f–h. Immature and mature asci. i. Ascospore. j, k Ascospores in Indian ink. Scale bars: b = 500 μm, c = 200 μm, d–I = 50 μm, j, k = 20 μm.

Notes: Alternariastercentaureae-diffusae is the first report of a sexual morph in the genus Alternariaster and is introduced as a new species based on both morphology and phylogeny. Alternariastercentaureae-diffusae forms a robust clade sister to A. bidentis and A. helianthi with high bootstrap support. Alternariaster centaureae-diffusae shares similarities with the family type of Leptosphaeriaceae,Leptosphaeria doliolum in having ascomata with a peridium of scleroplectenchymatous cells. Alternariastercentaureae-diffusae differs from Leptosphaeria and other genera in the family in having long filiform, multi-septate ascospores.