Stilbochaeta hainanensis W. M. Zhang & L. Lu, 2025

Zhang, Wangming, Feng, Qinying, Song, Xiaoyu, Zhou, Xinzhong, Xie, Wanqing, Lu, Juan & Lu, Li, 2025, Two new species of Stilbochaeta (Chaetosphaeriaceae, Chaetosphaeriales) from freshwater and terrestrial habitats in China, MycoKeys 121, pp. 67-78 : 67-78

Stilbochaeta hainanensis W. M. Zhang & L. Lu sp. nov.

Fig. 3

Etymology.

The epithet “ hainanensis ” refers to Hainan Province, China, where the fungus was collected.

Holotype.

GZAAS 25–0003 .

Description.

Saprobic on submerged decaying wood in a freshwater habitat. Sexual morph Undetermined. Asexual morph Hyphomycetous. Colonies on the natural substrate effuse, hairy, brown, with white, glistening conidial mass. Mycelium mostly immersed, composed of branched, septate, smooth, brown hyphae. Conidiophores 70–171 µm long, 3.5–6 µm wide at the base (x ̄ = 125.5 × 5 µm, n = 20), macronematous, mononematous, brown at the base, fading to pale brown towards the apex, septate, unbranched, cylindrical, erect, straight or slightly curved, thin-walled, smooth. Conidiogenous cells 11–26 µm long, 3–5.5 µm wide (x ̄ = 21 × 4.5 µm, n = 25), mono- or poly-phialidic integrated, terminal, determinate, clavate, ellipsoidal, collarette funnel-shaped. Conidia 8.5–14.5 µm long, 2.5–4 µm wide (x ̄ = 10.5 × 3.5 µm, n = 30), acrogenous, usually aggregated in slimy droplets, 1 - septate, guttules, subcylindrical, obclavate, fusiform to allantoid, slightly curved, hyaline.

Culture characteristics.

Conidia germinating on PDA within 11 h and germ tubes arising from the conidium. Colonies reached 38 mm diam. after 44 days of incubation at 25 ° C, irregular, with flat, white to pale brown mycelia on the surface, in reverse pale brown to brown, with undulate margin.

Material examined.

China, Hainan Province, Wuzhishan City , on submerged decaying wood in a freshwater habitat, 10 January 2025, Wang-Ming Zhang, W 25 ( GZAAS 25–0003 , holotype), ex-type living culture GZCC 25–0003 ; Ibid., W 27.3 ( GZAAS 25–0004 , paratype), living culture GZCC 25–0004 .

Notes.

Stilbochaeta hainanensis aligns with the asexual morphological species concept of the genus Stilbochaeta , as defined by Réblová et al. (2021) and Wu and Diao (2022). In our phylogenetic analysis (Fig. 1 ), Stilbochaeta hainanensis ( GZCC 25–0003 and GZCC 25–0004 ) clusters with S. cangshanensis ( MFLUCC 17–2214 , NN 047608 and NN 077955 ), S. malaysiana ( IMI 312436 , NN 076617 and NN 076748 ), S. novae-guineensis ( CBS 147515 ), S. ramulosetula ( IMI 313452 ) and S. septata ( CBS 143386 and CBS 146716 ). However, Stilbochaeta hainanensis (8.5–14.5 µm long conidia) differs from S. cangshanensis (15–18 µm long), S. malaysiana (21–26 µm long), S. novae-guineensis (14–19 µm long), S. ramulosetula (16–19.5 µm long) and S. septata (13.5–16 µm long) by having smaller conidia ( Réblová et al. 2021). In addition, Stilbochaeta hainanensis (70–171 µm long) can be distinguished from S. cangshanensis (39–53 µm long) and S. novae-guineensis (27.5–58 µm long) by its longer conidiophores ( Réblová et al. 2021). Furthermore, our isolates GZCC 25–0003 and GZCC 25–0004 form a strongly-supported monophyletic group with 100 % ML and 1.00 BYPP values, indicating they represent the same species. Within Stilbochaeta , this lineage is distinct from all previously known taxa. Therefore, based on multi-gene phylogenetic analyses, we introduce GZCC 25–0003 and GZCC 25–0004 as representing a new species, Stilbochaeta hainanensis .

Figures

Figure 1. Phylogenetic tree generated from the RAxML analysis, based on the combined dataset of LSU and ITS sequences. Bootstrap support values for ML (≥ 75 %) and BYPP (≥ 0.95) are indicated near their respective nodes. Codinaea assamica (CBS 139907) and C. dwaya (CBS 261.77) were selected as outgroup taxa. Ex-type and ex-epitype strains are denoted by “ T ” and “ E ”, respectively and newly-obtained isolates are indicated in bold red font. A dash (“ - ”) indicates bootstrap support values below 0.95 for BYPP.

Figure 3. Stilbochaeta hainanensis (GZAAS 25–0003, holotype). a, b. Colonies on the natural substrate; c – f. Conidiophores and conidiogenous cells bearing funnel-shaped collarettes; g – j. Conidiogenous cells; k – v. Conidia; w, x. Colonies on PDA from above and below. Scale bars: 50 μm (c, d); 30 μm (e, f); 10 μm (g – j); 5 μm (k – v).