Clypeostroma Theiss. & Syd., Annls mycol. 12(3): 272 (1914).
Index Fungorum number: IF 1128; Facesoffungi number: FoF 12167, 2 morphological species (Species Fungorum 2022), no molecular data available.
Saprobic on host. Sexual morph: Ascomata developing and maturing on lower surface of living leaves, forming black, tar-spot-like symptoms, more or less round in outline, slightly raised, tapering gradually to margin, often with numerous ascomata on a single leaf; no chlorosis of surrounding leaf tissue. Ascomatal surface black, more or less smooth, with tiny, round ostioles barely visible. Ascomata subcuticular, not becoming erumpent, with several pseudothecia covered by a single clypeus. Pseudothecia more or less globose, flattened cells with pale brown, thin walls; opening through a simple, round ostiole at apex. Upper part of pseudothecial wall merging with clypeus. Clypeus subcuticular, comprising 3-4 rows of angular cells with dark, thick walls. Scattered hyphae with thin, hyaline walls forming beneath clypeus, between and below pseudothecia and amongst the largely intact cells of the host leaf. Asci cylindric to subsaccate, tapering abruptly to small, foot-like base, and gradually to rounded apex, fissitunicate, 8-spored. Ascospores uniseptate, constricted slightly at the more or less central septum, upper cell slightly wider than lower, rounded at apex and base, wall becoming pale brown, sometimes finely punctate. Paraphyses not reported. Asexual morph: Unknown (adapted from Johnston 2002).
Type species: Clypeostroma spilomeum (Berk.) Theiss. & Syd.
Notes: Clypeostroma is characterised by subcuticular ascomata, more or less globose pseudothecia, cylindric to sub-saccate asci anduniseptate ascospores constricted slightly at the more or less central septum. Clypeostroma spilomeum was previously known as Dothidea spilomea found from Hebe elliptica in Auckland Islands and Campbell Island (Berkeley 1845). Cooke (1890) described another fungus found on the same host from Ewing Island as Rhytisma discoidea. Theissen and Sydow (1914) synonymized these two species and transferred another fungus observed by Berkeley (1845) to Clypeostroma as C. spilomeum. Hawksworth et al. (1995) listed Clypeostroma as a nomen dubium. Johnston (2002) reported that the two species described by Berkeley (1845) might represent two different fungi since D. spilomea had flatter ascomata tapering gradually to the margin, and larger ascospores. Clypeostroma might belong to Dothideales sensu Barr (1987) based on the lack of hamathecial tissue but the presence of immersed, globose, thin-walled pseudothecia aggregated beneath a common, subcuticular clypeus makes its systematic position ambiguous (Johnston 2002). Johnston (2002) re-collected C. spilomeum and provided an updated account of the genus. Molecular data is lacking for Clypeostroma. Clypeostroma is in Dothideomycetes genera incertae sedis. Fresh collections with DNA sequence data are needed to confirm the systematic position of this genus.