Exosporium rhapidis S.S. Xiang & C.L. Yang, in Yang, Li, Xiang, Xu, Zeng, Sun, Liu, Maharachchikumbura, Lv, Wang, Ji-Zuo, A-Niu & Liu, Mycosphere 16(1): 1894 (2025)

Index Fungorum number: IF900692; MycoBank number: MB900692; Facesoffungi number: FoF16127

Etymology – The specific epithet reflects the host genus Rhapis.

Holotype – SICAU 23-0132

Associated with brown leaf spots on leaves of Rhapis excelsa (Thunb.) Henry ex Rehd., spots amphigenous, circular, oval or irregular, confluent, necrotic surrounded by a brown to dark brown margin, sometimes entire spots brown to dark brown. Sexual morph: Not observed. Asexual morph: Hyphomycetous. Mycelium sparse, mainly internal. Stromata semi-immersed to immersed, globose or irregular, brown to dark brown. Conidiophores 45–175 × 3–5 μm (x̄ = 104 × 3.6 μm, n = 50), loose or denser fascicles, arising from stromata or hyphae, erect, straight, sometimes slightly curved, cylindrical, simple, rarely branched in the apex, regular in width, sometimes swollen cells in the base, uniformly medium brown to brown or more or less paler towards the apex, 0–7-septate, occasionally pluriseptate, smooth-walled, thickened. Conidiogenous cells 25–70 × 3–5 μm (x̄ = 47.3 × 3.6 μm, n = 50), integrated, terminal, sometimes intercalary, conidiogenous loci conspicuous, 1–3 μm diameter (x̄ = 2.1 μm, n = 50). Conidia 19–62 × 5–8 μm (x̄ = 43.4 × 6.1 μm, n = 50), solitary, obclavate-cylindrical, straight to slightly curved, 2–8-distoseptate, rarely 0–1- distoseptate, pale brown, smooth-walled, apex obtuse, base gradually or short obconically truncate, with darkened hila.

Culture characteristics – Colonies on PDA attaining 15–25 mm diameter in 3 weeks, dense, subcircular, crenated, coriaceous, grey to dull brown in the center, orange to dark orange toward the margin, aerial mycelia infrequent, reverse pale yellowish-brown, radially furrowed.

Material examined – China, Sichuan Province, Chengdu City, Wenjiang District, Schoolyard of Sichuan Agricultural University, 103°51′33.82″E 30°42′18.52″N, 528 m, isol. from leaves of Rhapis excelsa, 20 Nov. 2019, C.L. Yang, YCL201911001 (SICAU 23-0132, holotype), ex-type culture (SICAUCC 23-0101). ibid. YCL201911001-2 (SICAU 23-0167), living culture SICAUCC 23-0136.

GenBank numbers – SICAUCC 23-0101 = ITS: PP769687, LSU: PP719617, rpb2: PQ005609. SICAUCC 23-0136 = ITS: PP781968, LSU: PP719618, rpb2: PQ005612

Notes – Exosporium rhapidis is phylogenetically closer to E. livistonae and E. livistonicola, as supported by both maximum likelihood and Bayesian analysis. However, the sequence comparisons support them as distinct species. Exosporium rhapidis differs from E. livistonicola (MUCC 190) with a 98.3% (711/723, 0 gap) similarity in the LSU, with a 86.33% (423/490, 35 gaps) similarity in the ITS, and with a 92.77% (770/830, 0 gap) similarity in the rpb2 (Videira et al. 2017). Morphologically, E. rhapidis exhibits finer conidiophore cells (25–70 × 3–5 μm vs. 15–70 × 4–6 μm), smaller conidiogenous loci (1–3 µm vs. 3–4 μm), and shorter conidia (19–62 × 5–8 μm vs. 60–70 × 7–10 μm) compared to E. livistonae (Crous et al. 2011). Additionally, when compared to E. livistonicola, E. rhapidis shows variations in smaller conidiophores (45–175 × 3–5 µm vs. 40–280 × 3–6 µm) and longer conidiogenous cells (25–70 µm vs. 10–30 µm) (Braun et al. 2006, 2014). These distinctions lead us to introduce E. rhapidis as a new species.

Figure 1 – Exosporium rhapidis (holotype, SICAU 23-0132). a, b Symptoms on the leaf. c Appearance of conidiogenesis. d Conidiophores. e–h Conidiogenous cells with developing conidia. i–n Conidia. o Germinating conidium. p Front view of colony on PDA. q Reverse view of colony on PDA. Scale bars: c = 200 μm, d–g = 40 μm, h–o = 20 μm.