Roussoella
Roussoella Sacc., Atti dell´Istituto Veneto Scienze, 6: 410 (1888).
Index Fungorum number: IF 4799; Facesoffungi number: FoF 01689, 33 morphological species (Mapook et al. 2020, Phukhamsakda et al. 2020, Species Fungorum, 2022), 22 species with molecular data.
Saprobic on decaying bamboo culms or palms branches. Sexual morph: Ascostromata semi-immersed to immersed under a clypeus darkened, slightly raised, somewhat liner or dome-shaped areas, with a flush intra-epidermal papilla on host surface, gregarious; in vertical section subglobose with a flattened base. Peridium comprising several layers of elongate cells with interspersed brown melanin particles, dark brown at the outside. Hamathecium comprising 1–2 μm diam., numerous, anastomosing, hypha-like, septate, straight, cellular pseudoparaphyses, narrowing towards the ends, branching at the apex, embedded in a gelatinous matrix. Asci 4 to 8-spored, bitunicate, cylindrical, apically rounded, with a distinct ocular chamber. Ascospores overlapping uniseriate, fusiform-ellipsoidal, straight, 2-celled, constricted at the septum, brown, ornamented and surrounded by a wide mucilaginous sheath. Asexual morph: linked to Cytoplea (Hyde et al. 1996). Conidiomata pycnothyrial, superficial or semi-immersed, subglobose, dark-brown to black, multilocular, locules separated by vertical columns of darkly pigmented pseudoparenchyma. Peridium comprising several brown to dark brown layers with cells of textura angularis. Conidiophores reduced to conidiogenous cells, holoblastic discrete, hyaline, cylindrical to ellipsoidal, smooth, formed from cells lining the innermost later of the pycnidium. Conidia oblong ellipsoidal, narrower towards the apex, brown, thick-walled, often biguttulate, minutely warty (adapted from Liu et al. 2014).
Type species: Roussoella nitidula Sacc. & Paol.
Notes: Roussoella is characterised by semi-immersed to immersed ascostromata, bitunicate, cylindrical, apically rounded asci and fusiform-ellipsoidal, straight, two-celled ascospores surrounded by a wide mucilaginous sheath. The asexual morph is characterised by pycnothyrial, superficial or semi-immersed, subglobose conidiomata, holoblastic discrete, hyaline, cylindrical to ellipsoidal conidiophores and oblong-ellipsoidal conidia. Information regarding the type species of Roussoella, R. nitidula has been confusing (Liu et al. 2014). Höhnel (1919) transferred an earlier epithet Dothidea hysterioides to Roussoella and treated Roussoella hysterioides as type of the genus. This treatment was followed by several authors who listed R. hysterioides as the type of Roussoella (Müller & Arx 1962, Eriksson 1984, Hyde et al. 1996, Hyde 1997, Aptroot 1995, Tanaka et al. 2009, Hyde et al. 2013). Hyde et al. (1996) re-studied the type specimen of Dothidea hysterioides and Roussoella nitidula and synonymized them under Roussoella hysterioides. Liu et al. (2014) re-examined the type specimen of R. nitidula but was unable to borrow the type material of Dothidea hysterioides from PAD. The authors could not confirm that Dothidea hysterioides is identical to R. nitidula as the ascospores were smaller compared to those described in Hyde et al. (1996). Liu et al. (2014) also provided an epitype of R. nitidula with a fresh collection. Cytoplea, Neopycnodothis and Roussoella might be synonyms. Sutton’s description of Cytoplea is similar to those of the asexual morph of Roussoella but the conidia of C. arundinicola are reported to beuniseptate (Sutton 1980). The type species of Cytoplea, C. arundinicola was found from Arundo donax (Poaceae) from Italy while Sutton (1980) described it under the earlier epithet C. arundinacea. Cytoplea arundinicola must be epitypified and DNA sequence data must be obtained to confirm whether Cytoplea and Roussoella are synonyms or not. Based on this evidence, Liu et al. (2014) preferred to use Roussoella instead of Cytoplea. Roussoella is currently a distinct and type genus of Roussoellaceae. Molecular markers available for Roussoella include ITS, LSU, SSU, TEF-1 and RPB2.
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