A liverwort with striking receptacles growing on the inner edge of the pavement where it meets a garden wall.
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Thanks, Lavateraguy, that looks like a good match. As there is no median line on the thallus, that would make it subspecies montivagans, the Mountain Liverwort.
Lat/Lng: 51.381341666667, 0.00339
OS grid ref: TQ395666