Pilidium Kunze, in Kunze & Schmidt, Mykologische Hefte (Leipzig) 2: 92 (1823)
= Discohainesia Nannf., Nova Acta R. Soc. Scient. upsal., Ser. 4 8(no. 2): 88 (1932)
= Hainesia Ellis & Sacc., in Saccardo, Syll. fung. (Abellini) 3: 698 (1884)
= Sclerotiopsis Speg., Anal. Soc. cient. argent. 13(1): 14 (1882)
Facesoffungi number: FoF 07495
Leotiomycetes, Leotiomycetidae, Chaetomellales, Chaetomellaceae
Parasitic on the host plant or isolated from soil. Sexual morph: see Rossman et al. (2004). Asexual morph: Conidiomata pycnidial or sporodochial; pycnidia pale brown when young, dark brown to black at maturity, solitary to gregarious, subepidermal to epidermal, immersed to superficial, globose, subglobose, obpyriform or oblong, sessile, unilocular, glabrous. Ostiole indistinct, opening by a stellate slit or irregular rupture. Pycnidial wall composed of thick-walled, pale brown to dark brown cell of textura angularis in the exterior, gradually merging with hyaline cells in the conidial hymenium. Conidiophores formed from the inner wall layer of conidioma, hyaline, cylindrical, branched and septate at the base, smooth-walled. Conidiogenous cells hyaline, enteroblastic, phialidic, lageniform to cylindrical, usually integrated, determinate, smooth-walled, with a minute apical channel and collarette. Conidia hyaline, fusiform to falcate or cymbiform, with obtuse base and acute apex, unicellular, smooth-walled, eguttulate. Sporodochia pale luteous, solitary, superficial, globose to cupulate, discoid, with irregularly wavy margin, slimy, stalk pale brown near base, becoming dark brown at apex. Conidiophores, conidiogenous cells and conidia similar to those in pycnidia (adapted from Sutton 1980; Rossman et al. 2004).
Type species: Pilidium acerinum (Alb. & Schwein.) Kunze, in Kunze & Schmidt, Mykologische Hefte (Leipzig) 2: 92 (1823)
Notes: Pilidium is similar to Chaetomella in having two types of conidiomata (pycnidium or sporodochium), acropleurogenous conidiogenous cells, and hyaline, usually fusiform to falcate, unicellular conidia. However, Chaetomella was separated from Pilidium by its setose conidiomata and molecular data.
The nomenclatural and taxonomic history of Pilidium was provided by Shear and Dodge (1921). Sutton (1980) revised Pilidium and accepted two species, P. acerinum and P. concavum (Desm.) Höhn. Pilidium acerinum has been reported primarily on leaves of deciduous trees, e.g., Eucalyptus grandis (Crous 1991). This species was studied by Palm (1991) who determined that light-colored, fleshy, discoid, stalked sporodochia of Hainesia lythri is a synanamorph of the black, enclosed pycnidia of P. concavum (Rossman et al. 2004). The synonymy of Pilidium was provided by Sutton (1980), Rossman et al. (2004), Johnston et al. (2014) and Wijayawardene et al. (2017b) as Discohainesia, Hainesia and Sclerotiopsis.
Rossman et al. (2004) designated an epitype for P. acerinum and placed Pilidium in Chaetomellaceae (Leotiomycetes) based on molecular data. They also assigned the sexual morph of Pilidium to Discohainesia. Subsequently, several new species were included in the genus, P. pseudoconcavum Crous (2013), P. lythri (Desm.) Rossman (2014), P. eucalyptorum Crous & M.J. Wingf. (2015), P. septatum A. Giraldo & Crous (2017). Six taxa are accepted in the genus. Pilidium species are commonly plant pathogens causing leaf spots, root lesions and tan-brown rot of fruits or isolated from soil (Sutton and Gibson 1977; Rossman et al. 2004; Karimi et al. 2016; Groenewald et al. 2017).
Distribution: Austria, Brazil, Canada, China, Eire, France, Germany, Iran, Italy, Japan, Lithuania, Mozambique, New Zealand, Netherlands, Philippines, Portugal, Spain, South Africa, UK, USA, Thailand (Sutton 1980; Rossman et al. 2004; Crous et al. 2013, 2015, 2017; Karimi et al. 2016; Marin-Felix et al. 2017).
Pilidium acerinum (redrawn from Sutton 1980) a Conidiophores, conidiogenous cells and developing conidia. b Conidia. c Vertical section of conidioma.