Kirschsteiniothelia tumidula H. L. Si, R. L. Chang, T. Bose & Y. C. Wang 2025, sp. nov.

Kirschsteiniothelia tumidula H. L. Si, R. L. Chang, T. Bose & Y. C. Wang sp. nov. Fig. 5 j – r Etymology. The name refers to the convex colony of this fungus on PDA. Type. China • Yunnan Province, Chuxiong Yi Autonomous Prefecture, Chuxiong City, Dayao County (26°32'71.54"N, 100°57'3.6"E), isolated from the medullary tissue of the lichen Usnea aciculifera (SDCX 79), 13 Nov. 2020, H. L. Si, CX 79 B 2 = CGMCC 3.23629 (the ex-holotype culture), dried culture HMAS 352146 (holotype specimen), GenBank Accession Numbers: ITS OQ 645272; LSU OQ 645286; SSU OQ 645279. Description. Hyphae smooth, olivaceous in colour, branched, septate, measuring approximately 1.78–4.76 μm (x ̄ = 2.61, n = 50) in diam (Fig. 5 i-o). Conidiophores macronematous, mononematous, terminal or lateral, pale blue to olive green, smooth, unbranched, septate, measuring 34.07–70.85 × 5.11–10.06 μm (x ̄ = 50.63 × 7.17 μm, n = 11) (Fig. 5 m – o). Conidiogenous cells monoblastic, integrated, terminal, determinate, spherical or ovoid in shape, surface smooth, pale blue to olive green in colour, measuring 4.95–11.61 × 4.39–10.51 μm (x ̄ = 8.82 × 6.14 μm, n = 11) (Fig. 5 m-p). Conidia acrogenous, solitary, dry, pale olivaceous, pale at apex, septate, with 1–4 septa, slightly constricted at septum, obclavate, rostrate, smooth, straight or slightly curved, truncate at base, sometimes with a gelatinous sheath surrounding the apex, measuring 7.23–38.00 × 3.92–11.30 μm (x ̄ = 6.64 × 18.29 μm, n = 50) (Fig. 5 m – o). No sexual morph was observed. Culture characteristics. On PDA, after 7 days of incubation at 25 ° C, the colony is pale bluish green in the centre, the edge is grey, the centre is raised, the surface is tomentose, and the margin is entire (Fig. 5 j). The reverse of the colony is brown (Fig. 5 k). The optimal growth temperature is 25 ° C (5.86 mm / day). Slow growth (1.42 mm / day) was observed at 5 ° C, and no growth was detected at 30 ° C and 35 ° C. Host. Usnea aciculifera. Distribution. Yunnan, China. Note. Kirschsteiniothelia tumidula is phylogenetically close to K. aquatica, K. cangshanensis, K. longisporum, K. pini, and K. weiningensis. However, the Conidiophores of K. tumidula ranges between 34.07–70.85 μm are shorter than those of K. aquatica, K. cangshanensis, K. longisporum, K. pini, and K. weiningensis which range between 105.5–135.5 μm, 114–151 μm, 115–285 μm, 69–124 μm, and 75–125 μm, respectively (Bao et al. 2018; Jin et al. 2024; Tian et al. 2024; Xiao et al. 2025). Both K. tumidula, K. cangshanensis, and K. weiningensis exhibit a gelatinous sheath surrounding their apices, whereas K. aquatica, K. longisporum, and K. pini lack this feature. In addition, there is a significant variation in the ITS and LSU among these three species. There was a total of 37 bps (ITS: 34 bps, LSU: 3 bps, SSU: 0 bps) differences between K. tumidula and K. aquatica, 45 bps (ITS: 43 bps, LSU: 2 bps, SSU: 0 bps) differences between K. tumidula and K. cangshanensis, and 35 bps (ITS: 29 bps, LSU: 5 bps, SSU: 1 bps) differences between K. tumidula and K. longisporum, 39 bps (ITS: 36 bps, LSU: 3 bps, SSU: 0 bps) differences between K. tumidula and K. pini, and 43 bps (ITS: 36 bps, LSU: 6 bps, SSU: 1 bps) differences between K. tumidula and K. weiningensis.