Colonies restricted, slow-growing, brown or olivaceous. Aerial hyphae smooth- or somewhat rough-walled, pigmented. Cleistothecia up to 40 μm in diam, dark brown; peridium wall composed of textura angularis. Ascomata bearing antler-shaped appendages, with serrate edges. Asci bitunicate, clavate, 8-spored; ascospores pale brown, verruculose, 1–3-septate. Conidiophores reduced, unbranched or sparingly branched, arising from the aerial hyphae or hyphal ropes, continuous or septate, hyaline or pigmented, ovoid, clavate, wedge-shaped, cylindrical, or irregular. Conidiogenous cells scattered, monoblastic or sympodial, elongate to cylindrical. Conidia produced in clusters or acropetal series from the ends of tubular extensions of the conidiophores; conidia 1–4-celled, pigmented or hyaline, smooth or verrucose, ellipsoidal, ovoid, cylindrical, or T- or Y-shaped. (emended from Abbott 1927; Barron and Busch 1962; Seifert and Gams 2011; Samerpitak et al. 2014).

Abbott (1927) summarized the asexual features of Scolecobasidium as its generic character based on only two species S. terreum and S. constrictum. Over time multiple species of Scolecobasidium have been described, and the boundaries between this genus and closely related genera have also been clarified (Barron and Busch 1962; Seifert and Gams 2011; Samerpitak et al. 2014; Shen et al. 2020; Wei et al. 2022). However, no one has updated the generic character of Scolecobasidium. In this study, we update the generic character of Scolecobasidium based on previous descriptions, especially the morphological features of the sexual stage of the fungus.

Scolecobasidium terreum E.V. Abbott.

Named after the host plant Acanthus from which this fungus was isolated.

China. Guangdong Province: Qi’ao-Dangan Island Provincial Nature Reserve, from leaf of Acanthus ebracteatus, Nov 2019, M. Li, Z.F. Zhang and J.E. Huang (Holotype HMAS 352373, culture ex-type CGMCC 3.24352 = LC19368).

Sexual morph : unknown. Asexual morph: Mycelium consisting of branched, septate, hyaline to pale brown, smooth, and thick-walled hyphae. Conidiophores solitary, erect, brown, smooth, arising from superficial hyphae, subcylindrical, straight to geniculous, brown, thick-walled, 0(–2)-septate, 14.5–20.5 × 1.5–2 µm, often reduced to conidiogenous cells, bearing a few conidia near the apex. Conidiogenous cells brown, smooth, 4.5–9.5 × 1.5–2 µm, terminal and lateral on conidiophores, containing several apical, cylindrical denticles. Conidia 1-septate, smooth-walled, subhyaline to pale brown, cylindrical, rarely pyriform, constricted at the septum, 5.5–8.5 × 2.5–4 µm (av. ± SD = 6.9 ± 0.7 × 3.05 ± 0.2 µm, n = 42).

Colonies reaching up to 16–20 mm diam after 14 days at 25 °C, producing dense aerial mycelium on MEA and OA. On MEA, surface wheat to greyish brown, reverse saddlebrown, felty, dry, margins smooth. On OA, surface burlywood to peru, reverse brown black, margins smooth.

Figure 2. 

Scolecobasidium acanthi (ex-type CGMCC 3.24352) A the habitat of Acanthus ebracteatus B leaf spot on Acanthus ebracteatus C, D forward and reverse colony on OA after 14 days E, F forward and reverse colony on MEA after 14 days G–J conidiophores, conidiogenous cells and conidia K–P conidia. Scale bars: 10 μm (G–P).

Although represented by single strain, S. acanthi sp. nov. formed a distinct clade (Fig. 1) that was phylogenetically related to S. aegiceratis sp. nov. The two species differ from each other in 820/825 bp (99.39%) in LSU, 474/514 bp (92.22%) in ITS, 525/538 bp (97.58%) in tef1-α, and 433/464 bp (93.32%) in tub2. Morphologically, S. acanthi sp. nov. differs from S. aegiceratis sp. nov. in the septa number of conidiophores (0–2 vs. 0–1) and the size of conidiogenous cells (4.5–9.5 × 1.5–2 µm vs. 7.5–24 × 1.5–2.5 µm) and conidia (5.5–8.5 × 2.5–4 µm vs. 8–15(–26.5) × 2.5–3.5(–6.5) µm).

Named after the host plant Aegiceras from which this fungus was isolated.

China. Guangdong Province: Futian Mangrove National Nature Reserve, from leaf of Aegiceras corniculatum, July 2020, Z.F. Zhang (Holotype HMAS 352374, culture ex-type CGMCC 3.24353 = LC19369).

China. Guangdong Province: Futian Mangrove National Nature Reserve, from leaf of Aegiceras corniculatum, July 2020, Z.F. Zhang (Holotype HMAS 352375, culture ex-type CGMCC 3.24354 = LC19370).

Sexual morph : unknown. Asexual morph: Mycelium consisting of branched, septate, hyaline to pale brown, smooth, and thick-walled hyphae. Conidiophores arising from the aerial hyphae or hyphal ropes, continuous or septate, usually reduced to conidiogenous cells, 0(–1)-septate. Conidiogenous cells solitary, hyaline to pale brown, smooth, subcylindrical, straight to geniculous-sinuous, thick-walled, 7.5–24 × 1.5–2.5 µm, bearing a few conidia near the apex. Conidia smooth-walled, subhyaline to pale brown, ellipsoidal or cylindrical, tapering torwards the base, mostly 1-septate, rarely 2–3-septate, sometimes constricted at the septum, 8–15(–26.5) × 2.5–3.5(–6.5) µm (av. ± SD = 9.3 ± 1.16 × 2.83 ± 0.26 µm, n = 40).

Figure 3. 

Scolecobasidium aegiceratis (ex-type CGMCC 3.24353) A, B leaf spots of Aegiceras corniculatum C, D forward and reverse colony on OA after 14 days E, F forward and reverse colony on MEA after 14 days G–I conidiophores, conidiogenous cells and conidia J–M conidia. Scale bars: 10 μm (G–M).

Colonies reaching up to 20–22 mm diam after 14 days at 25 °C, dense aerial mycelium on MEA and OA. On MEA, smooth to felty, dry, surface greyish brown to dark brown, reverse saddle brown. On OA, surface ivory to peru, reverse brown black.

Scolecobasidium aegiceratis is phylogenetically related to S. dracaenae (Fig. 1) and can be differentiated from the later by DNA sequences of LSU (99.52% similarity), ITS (93.55%) and tef1-α (96.60%) regions. Morphological characters of the two species are overlapping but their conidiophores and conidia show differences. Scolecobasidium aegiceratis can be distinguished from S. dracaenae as it produces hyaline to pale brown (vs. brown in S. dracaenae) conidiogenous cells. In addition, the dimensions of their conidia (8–15(–26.5) × 2.5–3.5(–6.5) µm vs. 6.5–10 × 3–4 μm) and conidiogenous cells (7.5–24 × 1.5–2.5 µm vs. 5–15 × 2.5–3 μm) are different (Crous et al. 2016).

USA Louisiana, from soil, 1927, E.V. Abbott ex-type culture CBS 202.27 = MUCL 9471 (metabolically inactive).

Scolecobasidium constrictum was introduced at the same time as the generic type of Scolecobasidium, S. terreum, by Abbott (1927). Later, Heterosporium terrestre was treated as a synonym of S. constrictum due to their similar morphological characteristics (Barron and Busch 1962). Their original descriptions differ, however, in that H. terrestre produces rough conidia and variable conidiophores both in shape and size, and has occasional phragmospores. Therefore, Barron (1962) thought that Abbott described only a facet of S. constrictum and emended the species description. Subsequently, Ochroconis was introduced to accommodate species with sympodial conidiogenesis and unbranched, subspherical to cylindrical or clavate, melanised conidia, and S. constrictum was transferred to this genus as O. constricta and designated as the generic type (De Hoog 1973).

With the help of molecular analyses, Shen et al. (2020) synonymized Ochroconis under Scolecobasidium, and S. constrictum should be resurrected as a result. We observed that the ex-type cultures of H. terrestre (CBS 211.53) and S. constrictum (CBS 202.27) were separated into two distinct clades with relatively long branches in the current study (Fig. 1) and sequences similarities between the two species were very low (LSU: 98.7%; ITS: 88%, tef1-α: 85%, tub2: 79%). Since S. constrictum (CBS 202.27) is now sterile (Shen et al. 2020), we could only make a detailed morphological comparison among multiple descriptions of ex-type cultures of H. terrestre (CBS 211.53) and S. constrictum (CBS 202.27) (Abbott 1927; Atkinson 1952; Barron and Busch 1962; Samerpitak et al. 2014), and found that the two fungi were morphologically different in the shape (oval to ovate, short-cylindrical and long cylindrical to sole-shaped in H. terrestre vs. echinulate to verrucose in S. constrictum) and number of septa (0–3 vs. 0–1) in the conidia, as well as the size of conidiophores (2–31.5 × 1.5–2.5 μm vs. 5–8 × 2–2.5 μm). Based on morphology combined with the phylogeny, we consider that H. terrestre R.G. Atk. should not be treated as a synonym of S. constrictum, and a new combination Scolecobasidium terrestre comb. nov. is proposed in this study.

In addition, the type strain of S. constrictum should be CBS 202.27, rather than CBS 211.53, which was incorrectly listed in tables 2, 3 and figs 1, 2 in Wei et al. (2022).

Canada. Ontario: Ancaster, obtained from soil obtained, isolated by R.G. Atkinson, 31 Oct. 1947, holotype DAOM 28282, ex-type culture CBS 211.53 (= ATCC 11419; DAOM 28282; IMI 051380; MUCL 9896).

See the notes under S. constrictum.