I have gone through several books with field plants but I do not come across the plant.

Answer
Dear Hubert,
This is Physostegia virginiana (L.) Benth., a North American perennial from the lip flower family (Lamiaceae). She owes her Dutch name ‘Scharnierbloem’ to the fact that the individual flowers can be pushed to the side and retain this position for a long time.
Answered by
drs. Marc Reynders
Biology, systematics and evolution of seed plants. Specialized in tropical Cyperaceae.
http://www.ugent.be
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