Rhexocercosporidium senecionis Phutthacharoen & K.D. Hyde, in Hyde et al., Fungal Diversity 100: 155 (2020)
Index Fungorum number: IF556988; Facesofungi number: FoF 06820
Etymology: The specific epithet “senecionis” refers to the plant genus Senecio.
Holotype: MFLU 17–1635
Saprobic on dead stems. Sexual morph: Apothecia 150–300 × 100–200 μm (x̄ = 222.3 × 159 μm, n = 10), when dry arising singly or gregarious scattered on wood, sessile, rough surface, erumpent, black, with black setae surrounded. Receptacle concave. Disc flat, black. Margins light brown rounded, rough. Hairs up to 30–60 μm length (x̄ = 43.3 μm, n = 10), hyaline and dark brown, composed of thick-walled with septate. Ectal excipulum 30–50 μm (x̄ = 39.3 μm, n = 10) composed of thin-walled, 4–5 cell layers, lighter inwards, composed of cells of textura angularis. Medullary excipulum 15–25 μm (x̄ = 20.1 μm, n = 10), composed with hyaline cells of textura epidermoidea. Hymenium hyaline, inter mixed with asci and paraphyses. Paraphyses 2–3 μm wide (x̄ = 2.4 μm, n = 20), filiform, thin-walled, blunt end, aseptate. Asci 30–50 × 5–10 μm (x̄ = 39.5 × 7.5 μm, n = 20), 8-spored, unitunicate, inoperculate, cylindrical, thinwalled, short pedicellate, blunt apices, J +. Ascospores 5–10 × 2–3 μm (x̄ = 8.4 × 2.8 μm, n = 20), multi-seriate, fusiform to filiform, hyaline with 2–3 guttules, aseptate. Asexual morph: Undetermined.
Material examined: ITALY, Forlì-Cesena (FC), Campigna, Santa Sofia, on dying stems of Senecio nemorensis (Asteraceae), 3 September 2017, E. Camporesi, IT 3478b (MFLU 17–1635, holotype).
GenBank Numbers: ITS: MN688635, LSU: MN688633.
Note: Phylogenetically, our novel strain MFLU 17–1635 has a strong sister relationship to Pirottaea senecionis (CBS 307.58), but this latter strain is not related to any type material. Thus we introduce our collection as a new species. Further fresh collections of Pirottaea senecionis are needed to confirm their actual phylogenetic placement with DNA based sequence data. Rhexocercosporidium senecionis is distinct from other Rhexocercosporidium taxa by its apothecia that are surrounded by black setae and a light brown margin. Rhexocercosporidium sp. (MFLU 15–2755) also has a close phylogenetic relationship to Rhexocercosporidium senecionis. But, it has a different medullary excipulum. Rhexocercosporidium senecionis has textura epidermoidea in the medullary excipulum while Rhexocercosporidium sp. (MFLU 15–2755) has textura oblita. Rhexocercosporidium sp. (MFLU 16–0559) also clusters with other taxa in Rhexocercosporidium. It differs from R. senecionis by the features of medullary excipulum and the paraphyses that are swollen at the apex. Ascospores of MFLU 16–0559 are ellipsoidal and smooth whereas R. senecionis has fusiform to filiform ascospores with several guttules. Two other species of Rhexocercosporidium (R. carotae and R. panacis) are known only from their asexual morph and a comparison with R. senecionis is impossible.