found these markings on quite a lot of leaves in my garden
No identification made yet.
No interactions present.
... I suppose it could be the slime trail of a particularly large slug, going across the leaf?
If it were less regular, I might suggest that it's scorching, occuring when the sun shines on plants that have just been watered.
How to take close-ups with cheap phone and hand-lens:
Field Guides for Budding Botanists:
Lat/Lng: 53.076, -3.0265
OS grid ref: SJ313536
in my front garden