Acrocalymma hibisci G.O. Weerasinghe & K.D. Hyde, 2025

Acrocalymma hibisci G.O. Weerasinghe & K.D. Hyde , sp. nov.

Index Fungorum IF 903898, Facesoffungi FoF17781, Fig. 2 View FIGURE 2

Etymology: —The epithet refers to the host genus ( Hibiscus ) on which the fungus was collected.

Holotype: — MFLU 25-0067 View Materials

Saprobic on branches of Hibiscus rosa-sinensis L. Sexual morph:Undetermined. Asexual morph:Coelomycetous. Conidiomata 328–352 × 260–274 μm (x̄ = 340 × 265 μm, n = 5), pycnidial, immersed to erumpent, scattered, solitary, globose, ostiolate, dark brown to black. Pycnidia wall 34–40 µm (x̄ = 37 μm, n = 10) wide, of unequal thickness; thick outer layer and thin inner layer, composed of dark brown to hyaline textura angularis cells. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 6–8 × 8–11 μm (x̄ = 7.3 × 9.4 μm, n = 20), enteroblastic, phialidic, globose to subglobose, short, simple, aggregated, smooth, determinate, hyaline. Conidia 60–72 × 13–14 μm (x̄ = 66 × 14 μm, n = 35), unicellular, cylindrical, obtuse apex and narrow truncate base, straight with 7 transverse septa, thin, smooth walled, continuous to constricted at septa, with a bud scar surrounded by a small sheath like mucilaginous appendage at apex in immature stage.

Material examined: — THAILAND. Chiang Rai Province: Mae Fah Luang University, 20°02′42″N 99°53′41″E, on a dead branch of Hibiscus rosa-sinensis ( Malvaceae ), 7 January 2024, Zaw Lin Tun GO 60 ( MFLU 25-0067, holotype).

GenBank Accession Numbers: — ITS: PV272667, LSU: PV272668

Notes: —The multi-gene phylogenetic analysis of LSU, SSU and ITS sequences ( Fig. 1 View FIGURE 1 ) shows that our collection ( MFLU 25-0067) clustered with the strain ( MS 30), with 100% ML and 1 BPP support. BLASTn searches of the ITS sequence of MFLU 25-0067 resulted in 100% identity to fungal endophyte Acrocalymma sp. ( MS 30) ( Promputtha et al. 2005). However, morphological and ecological data related to MS 30 were not available in Promputtha et al. (2005). Thus, we consider MFLU 25-0067 ( holotype) and MS 30 as Acrocalymma hibisci . Acrocalymma hibisci formed an independent lineage sister to A. aquaticum ( MFLUCC 11-0208) with 63% ML and 0.91 BPP ( Fig. 1 View FIGURE 1 ) bootstrap support. According to the comparison of the pairwise genetic distance between Acrocalymma hibisci ( MFLU 25-0067) and its sister taxon Acrocalymma aquaticum ( MFLUCC 11-0208), there was 7.77% pairwise distance in the ITS region, corresponding to 30 base pair differences out of 386 bp. There was 1.23% base pair difference in LSU sequences, corresponding to 10 base pair differences out of 815 bp.

Acrocalymma hibisci differs from A. aquaticum by the size of the conidia, the number of septa and shape of conidiogenous cell ( Table 2). Acrocalymma aquaticum was isolated from submerged wood in a freshwater stream in Thailand (Zang et al. 2012, Calabon et al. 2023) while A. hibisci (MFLU 25-0067) was isolated from a dead branch of Hibiscus rosa-sinensis in Thailand. Based on phylogeny and morphological evidences A. hibisci is introduced as a new species.