Roussoella Sacc., Atti

Liu, Jian-Kui, Phookamsak, Rungtiwa, Dai, Dong-Qin, Tanaka, Kazuaki, Jones, Gareth, Xu, Jian-Chu, Chukeatirote, Ekachai & Hyde, Kevin D., 2014, Roussoellaceae, a new pleosporalean family to accommodate the genera Neoroussoella gen. nov., Roussoella and Roussoellopsis, Phytotaxa 181 (1), pp. 1-33 : 8-9

Roussoella Sacc., Atti dell´Istituto Veneto Scienze, 6: 410. 1888.

Possible synonyms

Cytoplea Bizz. & Sacc. , in Bizzozero, Atti Ist. Veneto Sci. lett. ed Arti, Sér. 3, 3: 307. 1885.

Neopycnodothis Tak. Kobay., Ann. phytopath. Soc. Japan 30: 154. 1965.

Type species. Roussoella nitidula Sacc. & Paol.

Saprobic on decaying bamboo culms or palms branches. Ascostromata semi-immersed to immerse 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 interdispersed brown melanin particles, dark brown at the outside. Hamathecium comprising 1–2 µm diam., numerous, anastoming, hypha-like, septate, straight, cellular pseudoparaphyses, narrowing towards the ends, branching at the apex, embedded in a gelatinous matix. 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 state is 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.

Notes: Roussoella is a genus occurring on monocotyledons (mainly palms and bamboo), with 12 accepted species ( Ju et al. 1996, Hyde 1997, Hyde et al. 1999, Zhou et al. 2003), and is characterized by immersed, gregarious, clypeate ascostromata containing trabeculate pseudoparaphyses embedded in a gel matrix, long cylindrical bitunicate asci without obvious fissitunicate dehiscence and brown, 2-celled ornamented ascospores ( Saccardo and Paoletti 1888, Höhnel 1919, Müller and Arx 1962, Hyde et al. 1996,1999, Zhou et al. 2003). There is confusion concerning the type species of Roussoella ( Saccardo and Paoletti 1888, Höhnel 1919, Müller and Arx 1962). The genus was introduced by Saccardo and Paoletti (1888) with R. nitidula as the type species. Höhnel (1919) found an earlier name Dothidea hysterioides Ces. , and transferred the fungus to Roussoella , and considered Roussoella hysterioides (Ces.) Höhn to be the type of the genus. Later authors ( Müller and Arx 1962, Eriksson 1984, Hyde et al. 1996, Hyde 1997, Aptroot 1995b, Tanaka et al. 2009, Hyde et al. 2013) followed this treatment and listed R. hysterioides as the type of Roussoella . However, Index Fungorum (2013) correctly lists the type as R. nitidula .

In this paper we observed the type of R. nitidula ( FIG. 4), but were unable to examine the type of Dothidea hysterioides , because PAD will no longer loan specimens for taxonomic study. When redescribing Roussoella, Hyde et al. (1996) examined the type materials of Dothidea hysterioides and Roussoella nitidula and listed them as synonyms using the earlier name Roussoella hysterioides as with most previous authors. The asci and ascospore sizes of the type material of Dothidea hysterioides or R. nitidula were not given in the study of Hyde et al. (1996). Measurements were mainly based on fresh collections. In this study, our collection of R. nitidula has smaller ascospores (17.5–21 × 5.5–8 µm), while Hyde et al. (1996) indicated ascospores of R. hysterioides as being 18–34 × 6–8 µm. Since we cannot confirm that Dothidea hysterioides is identical with R. nitidula we consider the latter to represent the genus type, and also epitypify R. nitidula with a fresh collection. The status of R. hysterioides is presently unclear.

Cytoplea , Neopycnodothis and Roussoella are probably synonymous. The type of Cytoplea , C. arundinicola Bizz. & Sacc. was described from Arundo donax (grass, Poaceae ) from Italy and Sutton (1980) illustrated it under the earlier name C. arundinacea (Sacc.) Petr. & Syd. Sutton’s account is typical of asexual Roussoella ; however, in the protologue of C. arundinicola , conidia are described as 1-septate ( Sutton 1980). Cytoplea arundinicola therefore needs to be restudied, recollected, epitypified and subjected to phylogenetic analysis before this genus can be used to accommodate Roussoella species. For this reason we use Roussoella rather than Cytoplea to represent the genus. Neopycnodothis is monotypic and was described from Phyllostachys edulis (Carrière) J.Houz (bamboo, Graminae) and appears to be a species of Roussoella .