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How do you distinguish the Agrimonia spp. before they have fruits?
The short answer is "You shouldn't", by photos anyway. It is a statistical guess based on their relative frequency. In the field you need to look for glands on the leaf underside for A. procera. However, John Poland says petals notched for procera and entire for eupatorium which fits the photo! Phew!
Lat/Lng: 52.239994049072, -1.709489941597
OS grid ref: SP199602