Phaeocytostroma saprophyticum P.C. Ding, Madhushan & Maharachch., 2025

Phaeocytostroma saprophyticum P.C. Ding, Madhushan & Maharachch. , sp. nov. ( FIGURE 3 View FIGURE 3 )

MycoBank: MB 859478

Etymology: Refers to the saprophytic lifestyle of the fungus

Asexual morph : Conidiomata 245–995 × 212–424 μm ( x̄ = 418 × 259 μm, n = 30) acervular, irregularly discoid in shape, produced singly, black, initially immersed in clypeus, protruding through the host surface unilocular. Conidiomata wall 13–87 μm ( x̄ = 32.46 μm, n = 30) thick, composed of irregular brown fish - scale - like tissues. Paraphyses rare, narrow and slender, hyaline, with air bubbles. Conidiogenous cells 10.5–23.4 × 1.1–3.3 μm ( x̄ = 14.78 × 2.15 μm, n = 30) tightly aggregated at the base, cylindrical to ampulliform, wider at the base and tapering towards the apex, hyaline. Conidia 6.1–11.9 × 1.4–3.6 μm ( x̄ = 9.71 × 2.54 μm, n = 50) are elongated - circular, grey, with a thick and dark - black wall, and contain guttules, black spore masses are copious, strongly erumpent, forming large, hard globular masses over the line of dehiscence, rarely spreading. Sexual morph : Not observed

Colony characteristics: Conidia germinate on the PDA in 48 h at 24°C. Colonies on PDA reached 41cm diam. after 15 days at 24 °C, surface effuse, sparse, entire edge, circular, sparse periphery, dark brown in surface, dark brown to black in reverse.

Materials examined: China, Sichuan Province, Mianyang City, Jiangyou County, Wu Du Town , 104.771110 N, 31.913205 E, 20 November 2024, P.C. Ding ( HKAS 148724 View Materials , holotype; isotype HUEST 25.0053 ), ex type CGMCC 3.28974 View Materials = UESTCC 25.0114 .

Notes: In the multi-gene phylogenetic tree ( FIGURE 2 View FIGURE 2 ), Phaeocytostroma saprophyticum forms a distinct clade and is phylogenetically closest to strains putatively labelled “ Phaeocytostroma sacchari ” (UMICH-1, km-1, CBS 275.34, and 135) and Pseudophaeocytostroma bambusicola (JM 2022a BN14, and JM 2022a BN17). Phaeocytostroma sacchari was originally described based on morphological features ( Sutton et al. 1964), However, its sequence data was first provided by Lamprecht et al. (2011) from a strain (CBS 275.34) isolated in Japan. However, that strain lacks host information and was not accompanied by a morphological description. Therefore, its identity remains uncertain, and further studies incorporating both morphology and molecular data are needed to resolve the taxonomy and variation within this species. Monkai et al. (2022) found that there were no significant differences in the morphological characteristics between the newly introduced Pseudophaeocytostroma and the genus Phaeocytostroma . Therefore, they introduced it based on the fact that Pseudophaeocytostroma clustered with Pustulomyces in their phylogenetic analysis, and with strong evidence of phylogenetic incongruence with other related genera (viz. Phaeocytostroma , Pustulomyces , Massariothea and Stenocarpella ). Furthermore, due to the unavailability of the type strain of P. sacchari , the strains CBS 275.34, km-1, UMICH-1 and 135 of P. sacchari were identified as “ Phaeocytostroma sacchari ”. Therefore, the genus Pseudophaeocytostroma was introduced as a new genus in the family Diaporthaceae . In our study, ITS sequence data suggest a relationship to these strains, the LSU and tef1-α trees place P. saprophyticum closer to Pse. Bambusicola ( FIGURE 1a–c View FIGURE 1 ), indicating topological incongruence among loci. Morphologically, P. saprophyticum resembles both type descriptions of P. sacchari and Pse. bambusicola , with brown, aseptate, ellipsoidal conidia. However, it differs by having more slender and shorter conidia (1.5–3.7 μm wide × 6.2–11.9 μm long), compared to P. sacchari (3–5 μm × 11–14.5 μm) and Pse. bambusicola (3–4.5 μm × 9–13 μm). In P. saprophyticum , conidia fill the entire locule. Additionally, P. saprophyticum has sparse paraphyses, in contrast to the abundant paraphyses seen in P. sacchari and Pse. bambusicola ( Sutton 1964, 1981). Its conidiomata are smaller (418.4 × 259.5 μm) than those of P. sacchari (650 × 350 μm) and Pse. bambusicola (250–704 × 89–420 μm). The ITS sequences of strain P. saprophyticum show a 97% similarity to those of Pse. bambusicola , with 561 of 576 bases, with 4 gaps. The tef1-α sequence of strain P. saprophyticum shows a 91% similarity to those of Pse. bambusicola , with 269 of 293 bases, with 4 gaps. Together, these phylogenetic and morphological differences support the recognition of our collection as a novel species. However, it is evident that the genus Phaeocytostroma is polyphyletic, or that the gene regions used are incongruent, as supported by our single-gene analyses ( FIGURE 1a–c View FIGURE 1 ), where other species assigned to Phaeocytostroma also cluster in different parts of the tree. This raises the question of whether those species should also be segregated into new genera, as was done for Pseudophaeocytostroma . To avoid further taxonomic confusion in the absence of clear morphological and molecular boundaries, we prefer to treat our species under Phaeocytostroma rather than introducing it under Pseudophaeocytostroma at this stage.