Bryonectria callicarpa

Hosts: Frullania dilatata

Two yellow-orange ascomata in the centre of the image at the ventral leaf margin. May 2024, Wiltshire.
Micrographs in water (except bottom left in lactophenol cotton blue) using oil immersion (1000X). Ventnor Down, VC10, Aug 2018. Ascospores initially 8-spored, but during development 4 spores degenerate so only 4 reach maturity.

Notes: This fungus can be found on the ventral (underside) surface of Frullania dilatata, especially on large mats. In my experience, it is impossible to spot in the field, requiring the collection of host fragments and their screening under a dissecting microscope – though infected plants may be overgrown with algae. The tiny yellow to orange, smooth fruitbodies are difficult to spot even then.