Anamorph: conidiomata pycnidia, to 400 µm diam., scattered or in small clusters, black, erumpent, ± globose, exuding hyaline, often opaque conidial masses. Conidiomatal wall of several layers of thick-walled angular cells, with an inner layer of hyaline cells. Ostiole central, to 40 μm diam. Conidiophores 10–25 × 4–5 μm, ± cylindrical to ampulliform, composed of one or two supporting cells, branched at the base or not; sometimes absent with the conidiogenous cells formed directly from the wall. Conidiogenous cells 8–20 × 3–4 μm, terminal, ± cylindrical, hyaline, smooth, coated in a mucoid layer, proliferating percurrently. Conidia (12–) 13–14 (–15) × 9–11 μm, solitary, broadly ellipsoidal, tapering towards a narrow truncate base 2–3 μm diam.; hyaline, aseptate, thin- and smooth-walled, coarsely guttulate or with a single large central guttule, enclosed in a persistent mucoid sheath 2–3 μm thick, usually with a hyaline, apical mucoid appendage (10–) 12–15 (–20) × 1.5–2 μm, flexible, unbranched, tapering towards an acutely rounded tip.
Teleomorph: ascostromata perithecial, 250-300 µm diam. and 200-250 µm high, externally similar to the conidiomata, erumpent, black, fairly thick-walled. Interascal tissue not present. Asci 80-120 x 17-25 µm, thick-walled and fissitunicate, 8-spored. Ascospores 16-24 x 8-12 µm, ellipsoidal to ovoid, hyaline, aseptate, thick- and smooth-walled, with cushion-shaped apical and basal gelatinous appendages.
Not formally assessed. It should almost certainly be assessed as Data Deficient.
A weak pathogen or secondary invader of leaves and small twigs of Taxus baccata.
Assuming that FRDBI records currently listed as Guignardia philoprina belong to this species [accessed May 2017], Phyllosticta foliorum is scattered throughout the British Isles from SE England to VC96 E Ness, with single records from Wales and ROI.