MycoBank: MB849595

Holotype: IRAN, Khuzestan Province, Ahvaz, isolated from rotten root of Phoenix dactylifera (Palmaceae), May 2021, M. Amani (holotype, IRAN 18302F; ex-type cultures, IRAN 4860C = SCUA-Am-A29).

Etymology. The species epithet “ palmarum ” reflects the host plant.

Asexual morph on PDA: Hyphae hyaline, septate, branched, 1.5–2.5 µm in diam. Sporulation from lateral phialidic pegs not observed. Conidiophores arose laterally from aerial hyphae, hyaline, straight or slightly curved, subcylindrical, commonly unbranched, but rarely one-times dichotomously branched, 0–2(–3)-septate, smooth, (16.5–)24.5–54.5(–60) × (1.2)1.8–2.6 μm, 95% confidence limits = 34.5–39.5 × 2.1–2.2 μm, (x̅ ± SD = 36.5 ± 9.8 × 2.1 ± 0.3 μm, n = 60), terminating in one or two conidiogenous cells. Conidiogenous cells terminal, hyaline, smooth, cylindrical to subulate, tapering towards apex (11.5–)14.5–37.5(–48) × 1.2–2.5 μm, 95% confidence limits = 21.5–25 × 1.8–1.9 μm, (x̅ ± SD = 23 ± 7 × 1.9 ± 0.3 μm, n = 60), apex 0.6–1.2 μm in diam. Conidia formed abundantly in slimy heads at apex of conidiogenous cells, aseptate, ellipsoidal to fusiform or falcate, curved, smooth, pointed at both ends, (2.9–)3.1–9.9 × 1–2.1 µm, 95% confidence limits = 5.1–6 × 1.3–1.5 μm, (x̅ ± SD = 5.5 ± 1.7 × 1.4 ± 0.3 μm, n = 60). Chlamydospores not observed. Sexual morph: not observed.

Culture characteristics—The colonies diameter on PDA, CMA, and OA were 43–46, 56–62, and 19–20 mm after 14 days of incubation at 25 ± 1° C, respectively. Colonies on PDA circular with filiform margin, pale vinaceous to rosy vinaceous, floccose with abundant aerial mycelium; reverse pale vinaceous. Colonies on CMA circular with regular margin, white, floccose, radiate, with aerial mycelium; reverse pale vinaceous. Colonies on OA circular with undulate to entire margin, white, cottony with abundant aerial mycelium; reverse white to pale vinaceous.

Additional materials examined. IRAN, Khuzestan Province, Karoon, isolated from rotten root of P. dactylifera, Sep. 2021, M. Amani (SCUA-Am-A29-1, SCUA-Ama-A29-2, and SCUA-Ama-A30); Bushehr Province, Ab pakhsh, isolated from rotten root of P. dactylifera, Sep. 2023, M. Amani ( SCUA-Ama-A30-1, SCUA-Ama-A30-2).

Notes: Phylogenetically, Xenoacremonium palmarum sp. nov., grouped with X. allantoideum, X. falcatum and X. minutisporum (Fig. 1). Nucleotide comparison of X. palmarum with X. falcatum revealed that these two species share 97% sequence identity in the tub2 gene (335 bp) attributed to 9 SNPs and 2 bp insertion/deletion, and 90 % sequence identity in the tef1α gene (420 bp) attributed to 21 SNPs and 22 bp insertion/deletion. In addition, X. palmarum and X. minutisporum shared 93.2 % sequence identity in the tef1α gene (265 bp) attributed to 10 SNPs and 8 bp insertion/ deletion. Both X. allantoideum and X. palmarum differ from X. falcatum and X. minutisporum in not having lateral phialidic pegs on its somatic hyphae, a feature which has not also been reported for X. recifei (Gams, 1971, Lombard et al. 2015, Roeun et al. 2022, Hou et al. 2023). Conidia in X. falcatum are more curved than those in X. palmarum and X. minutisporum (Gams 1971, Lombard et al. 2015). Furthermore, X. palmarum differs from X. allantoideum in having longer conidia (3.1–9.9 vs 3.6–6 μm) and by the lack of mycelial ropes and verticillately branched conidiophores (Hou et al. 2023).