Didymosphaeria futilis (Berk.& Broome) Rehm, Hedwigia 18: 167 (1879) (Fig 5)
Basionym: Sphaeria futilis Berk. & Broome, Ann. Mag. nat. Hist., Ser. 2 9: 326 (1852).
Index Fungorum number: IF 223613; MycoBank number: MB 223613; Facesoffungi number: FoF 00037
Saprobic on dead wood. Sexual state: Ascomata 110–140 × 120–160 μm (x̄ = 130 × 140 µm, n = 10), scattered, or in small groups, immersed to slightly erumpent, rarely nearly superficial, under a clypeus, globose to subglobose, membraneous, papillate. Papilla black, with a pore-like ostiole, ostiolar canal filled with periphyses. Peridium 10–20 μm (x̄ = 15 µm, n = 10) wide, 1-layered, composed of hyaline pseudoparenchymatous compressed cells of textura intricata, fusing at the outside with the host. Hamathecium of dense, 0.5–1 μm (x̄ = 0.8 µm, n = 20) broad, long, trabeculate pseudoparaphyses, anastomosing frequently above the asci, embedded in mucilage. Asci 75–85 × 4–6 μm (x̄ = 78 × 6 µm, n = 20), 8-spored, bitunicate, fissitunicate, cylindrical, pedicellate, rounded at the apex with an indistinct ocular chamber. Ascospores 7–10 × 3–5 μm (x̄ = 9 × 5 µm, n = 40), uniseriate, slightly overlapping, ellipsoid with obtuse ends, brown, 1-septate, slightly to not constricted at the septum, with distinctly spinulose ornamentation.Asexual state: unknown.
Material examined – UK. England: Norfolk, on dead stems of Rosa sp. (Rosaceae), March 1850, M.J. Berkeley (K 147683, holotype of Sphaeria futilis).
Fig. 1 Didymosphaeria futilis (K 147683, holotype of Sphaeria futilis). a–b Fungus on the host. c Section through ascoma. d Close-up of peridium.e Broad, long trabeculate pseudoparaphyses, anastomosing mostly above the asci. f–h Cylindrical asci with an indistinct ocular chamber. i–l Ascospores with distinct spinulose ornamentation. Scale bars: c = 100 µm, d = 10 µm, e, f–h = 20 µm, i–l = 5 µm.
Notes – Didymosphaeria sensu lato, introduced for three species of ascomycetes with 2-celled ascospores, comprise species having a wide distribution and a broad host range. Saccardo (1882) restricted the genus to only those species with brown ascospores. Aptroot (1995) included over 400 epithets of Didymosphaeria in his monograph of the genus after examining over 3,000 species, but only seven species were accepted. The placement of Didymosphaeria is confused as described in Ariyawansa et al. (2014b). Sivanesan (1984) reported that Didymosphaeria has Ascochyta and Periconia asexual states, while Kirk et al. (2008) reported Fusicladiella-like and Phoma-like species. Linking Didymosphaeria to asexual states should be treated with caution until the type of D. futilis has been sequenced. Ariyawansa et al. (2014b)found that two strains of the D. rubi-ulmifolii clustered in the family Montagnulaceae, but were separated from other genera of the family with high bootstrap support. Comparison of the generic type, D. futilis, and D. rubi-ulmifolii shows that they have similar morphology and thus represent Didymosphaeria. Thus Ariyawansa et al. (2014b)suggested that, based on the available molecular data and morphology, Didymosphaeria can be referred to Montagnulaceae with Didymosphaeriaceae as the probable synonym of Didymosphaeriaceae. In this paper, we formally treat Didymosphaeriaceae as a separate family in the order Pleosporales and with Montagnulaceae as its synonymy. The generic type of Didymosphaeria, D. futilis needs to be recollected, epitypified and sequenced so that phylogenetic analysis can be used to confirm family relationships within Pleosporales.
In the present study, we observed that the type strain of Paraconiothyrium brasiliense (CBS 100299) strain forms a robust clade with D. rubi-ulmifolii. Paraconiothyrium brasiliense was isolated from coffee fruits in Brazil, but this species has since been reported from various habitats in other continents, on woody and herbaceous host plants, such as Prunus spp. in South Africa (Damm et al. 2008). Near-identical ITS sequences have been deposited in GenBank for endophytes isolated from Ginkgo biloba (DQ094168), Juniperus virginiana (Hoffman and Arnold 2008), and Ulmus davidiana var. japonica (AB665311), and also from the herb Alliaria petiolata (EF432267). Strain CBS 395.87 from soil sampled in Italy was identified as Parac. brasiliense by Verkley et al. (2014). Verkley et al. (2014) showed that the ACT and TUB sequences of several Parac. brasiliense strains used in their study were more variable than in other related species, suggesting that Parac. brasiliense could be a species complex. In this study, we consider that Parac. brasiliense and Didymosphaeriarubi-ulmifolii are the same species as they cluster with high bootstrap support. We therefore synonymise these species. The only available name for this species is Didymosphaeriarubi-ulmifolii because Didymosphaeria brasiliensis is already in use.