Acrocalymma bipolare Abdel-Aziz & Abdel-Wahab
Index Fungorum number: IF557901; Facesoffungi number: FoF09243
Etymology: in reference to the polar mucoid appendages of the conidia
Holotype: CBS H-22673
Saprobic on submerged wood in freshwater habitats. Sexual morph: Undetermined. Asexual morph: Pycnidia 175–230 µm diam., globose or subglobose, erumpent to superficial, solitary, dark brown to black, without ostiolate papilla. Peridium 8–17 µm thick, composed of 8–11 layers of dark brown to black, thick-walled, cells of textura angularis, inwardly with narrow lumens, hyaline and thin-walled cells. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 2.5–7 × 2–3.5 μm, holoblastic, determinate, discrete, cylindrical or lageniform, hyaline, formed from the inner cells of the pycnidial wall. Conidia 9–12 × 3–5 µm (x̄ = 10.8 × 4.3, n = 50), cylindrical to fusiform, straight, unicellular, hyaline, thin-walled, guttulate, with rounded apex and slightly narrow, truncate base, with mucoid polar appendages that filled with oil droplets, appendages elongate in water to form filaments. Apical appendages 4–6 μm diam., rounded. Lower appendages 1–2 μm in length, sometimes split in the middle. (Descriptions from Dong et al. 2020)
Culture characteristics: Colonies on PDA up to 22 mm diam. after 2 weeks at 23 °C, with grey to dark brown aerial and immersed mycelium; reverse dark–brown.
Material examined: EGYPT, Sohag City, River Nile, 26°33′32ʺN, 31°41′44ʺE, on decaying wood submerged in River Nile water, 14 August 2012, F.A. Abdel-Aziz, (CBS H-22673, holotype), ex-type living culture MD1321.
Notes: Acrocalymma bipolare clusters with the type species A. medicaginis and A. pterocarpi Jayasiri et al. with high bootstrap support. Morphologically, Acrocalymma bipolare is different from A. medicaginis by its appendages that are filled with oil droplets and become filaments when mounted in water, while A. medicaginis processes globose to hemispherical or helmet-shaped appendages which do not form filaments in water (Alcorn and Irwin 1987). In addition, A. bipolare has shorter conidia than A. medicaginis (9–12 × 3–5 µm vs. 11–21 × 3.5–5 µm). The phylogenetically close species A. pterocarpi did not produce asexual morph in culture, thus their morphology cannot be compared (Jayasiri et al. 2019). Acrocalymma bipolare only has LSU sequence data, and it has four and six nucleotide differences with A. medicaginis and A. pterocarpi, respectively, which indicates them to be different species. This is also supported by the phylogenetic analysis of Dong et al. (2020). Acrocalymma bipolare differs from the other freshwater species A. aquatica in having shorter conidia (9–12 × 3–5 μm vs. 12–17 × 3–4 μm) and bipolar appendages compared with a single appendage in A. aquatica (Zhang et al. 2012). (Notes from Dong et al. 2020)
Fig. 1 Acrocalymma bipolare (CBS H-22673, holotype). a. Vertical section of a pycnidium. b. Section through the peridium. c–f. Variously shaped conidia with mucoid polar appendages. Note the apical appendages formed long filament (arrowed in d, stained in toluidine blue). Scale bars: a = 50 μm, b, c = 10 μm, d–f = 5 μm
Alcorn JL, Irwin JAG (1987) Acrocalymma medicaginis gen. et sp. nov. causing root and crown rot of Medicago sativa in Australia. Trans Brit Mycol Soc 88:163–167
Jayasiri SC, Hyde KD, Jones EBG, McKenzie EHC, Jeewon R, Phillips AJL, Bhat DJ, Wanasinghe DN, Liu JK, Lu YZ, Kang JC, Xu JC, Karunarathna SC (2019) Diversity, morphology and molecular phylogeny of Dothideomycetes on decaying wild seed pods and fruits. Mycosphere 10:1–186
Zhang H, Hyde KD, Mckenzie EHC, Bahkali AH, Zhou DQ (2012) Sequence data reveals phylogenetic affinities of Acrocalymma aquatica sp. nov., Aquasubmersa mircensis gen. et sp. nov. and Clohesyomyces aquaticus (freshwater coelomycetes). Cryptogam Mycol 33:333–346