Helminthosporium taiwannense K.C. Chang, S.Y. Hsieh, Goh & C.H. Kuo, sp. nov.
Figs. 4, 5
MycoBank: MB 860830
Etymology:— taiwanense, referring to the locality (Taiwan) where this species was collected.
Diagnosis:— Differs from other Helminthosporium species in having subhyaline, cylindrical conidia that are often borne in short chains.
Specimens examined:— TAIWAN. Nantou County, Ren’ai Township (24.15639 –121.1764, 1130 m a.s.l.), on decaying wood submerged in a freshwater stream, 13 November 2024, Chang-Hsin Kuo leg., NCYU-113RA1-2B1 (TNM: F0038890, holotype); ex-type cultures: BCRC-FU32133; DDBJ: LSU = LC893421, ITS = LC893420, SSU = LC893422, tef1-α = LC893423, rpb2 = LC893424.
Description:— Saprobic on decaying submerged wood in freshwater. Asexual morph: Colonies on the natural substrate effuse, velvety, greyish. Mycelium mostly immersed, composed of septate, branched, smooth, thick-walled, pale brown hyphae. Conidiophores macronematous, mononematous, solitary, erect, straight to slightly flexuous, unbranched, cylindrical, 265–720 μm long (x̄ = 473.5 μm, n = 25), with a swollen base (22–40 μm wide), 11–15 μm wide at the lower portion, tapering to 6.5–9.5 μm wide towards the apex, 9–12-septate, smooth-walled, dark brown, becoming slightly paler towards the apex. Conidiogenous cells mono- to polytretic, integrated, terminal and intercalary, cylindrical; tretic pores distinct, non-cicatrized, 2–3 μm in diam., formed just below the septa. Conidia acropleurogenous, solitary or formed in short, branched, easily disarticulating chains, subhyaline, concolourous, cylindrical, straight, 23–40 × 5.5–7.5 μm (x̄ = 33 × 6 μm, n = 25), with a rounded apex and an obconically truncate base bearing a distinct, dark hilum 2–2.5 μm wide, (3-)4–5(-6)-distoseptate, wall smooth. Conidial secession schizolytic. Sexual morph: Undetermined.
Notes:— Helminthosporium taiwanense is morphologically distinct within the genus.While most Helminthosporium species produce brown, obclavate, and typically solitary conidia (Liu et al. 2022), H. taiwanense is characterized by subhyaline, cylindrical conidia borne in short chains. Few species share this cylindrical to subcylindrical conidial shape. Helminthosporium livistonae Crous produces subhyaline, subcylindrical conidia but differs as they are solitary and not borne in chains; it is also associated with leaf spots on palms (Crous et al. 2018). Similarly, H. kalopanacis Gornostaĭ and H. matsushimae D.W. Li, Kai Zhang & R.F. Castañeda produce cylindrical conidia, but these are solitary and medium to dark brown (Gornostaĭ 1972, Matsushima 1993, Hu et al. 2023). Phylogenetically, our analyses indicate a close relationship with H. submersum Z.L. Luo, et al. (Zhao et al. 2018). However, H. submersum is readily distinguished by its production of brown, obclavate, and solitary conidia.
Under SEM observation, conidial catenation in H. taiwanense is apparent (Fig. 5). Following the production of a primary conidium, multiple subsequent conidia emerge as blown-out structures from its base or apex (Figs 5e, 5f). A single primary conidium can give rise to several subsequent conidia as "branches" (Fig. 51a), or it can produce several conidia in short chains (Fig. 5b). These chains or branches are easily disarticulated, leaving minute secession scars on the primary conidia (Fig. 5d) that are not visible under a light microscope. Conidial secession is schizolytic, as evidenced by the flush hilum at the conidial base (Fig. 5i). Figures 5c and 5h also reveals the conidiogenous pores (secession scars) on the conidiophores.
Publication Date: 2025-11-06