Anamorph: Conidiomata to 1 mm diam, eustromatic, immersed, subperidermal, multilocular or convoluted, with a dark brown wall, rupturing irregularly to allow spore release. Conidiophores to 25 µm x 2.5-4 µm, hyaline, smooth, septate and branched, with conidia formed from fertile loci at the apex of terminal or laterally at the apex of intercalary cells, proliferating percurrently with a minute collarette. Conidia 13.5-15.5 x 3-3.5 µm, fusiform, hyaline, smooth, with a ± median septum, lacking a gelatinous sheath or appendages.
Teleomorph: Stromata as pustules 1-4 mm broad, usually small but widely erumpent, sometimes confluent in longitudinal series, stromatic hyphae sparse, ectostromatic disc light-coloured when fresh but usually absent, usually containing 4-25 ascomata. Ascomata 400-550 µm diam, necks 450-900 x 100- 150 µm, elongate and sinous, transversely flattened when dry. Peridium 30-42 µm thick. Asci 40-54 x 7-11 µm. Ascospores 14-20 x 2-3 µm, slightly constricted at the median or slightly submedian septum, without appendages, 4-guttulate, lacking a gelatinous sheath or appendages.
Description contributed by Graham Kinsey, CABI. This species is more commonly named as Cryptodiaporthe hystrix due to its development in bark as well as leaf tissue and its ascospores that are hardly submedian, but stromatic development is restricted and molecular data indicate that a placement in Apiognomonia is justified (Sogonov et al., 2008). Collections on leaves have also been identified as Gnomonia cerastis, but that species is considered to be a synonym of Ophiognomonia ischnostyla. The anamorph has been referred to as Diplodina acerina (Sutton, 1980).