Dark River

The film is very loosely based on Rose Tremain's novel Trespass. Writer/director Clio Barnard wrote an initial screenplay that was much closer to the book, which focuses on two sets of of siblings in their sixties who become involved in a property dispute in France. After the initial draft, her producers encouraged her to make the story her own so that the final film, which focuses on only one set of siblings in their thirties and is set in England is only very loosely related to the book.

Joe shows Alice some shepherd's needle growing in a field. But the plant he shows her doesn't look like it (e.g. it's too big and too robust) and it wouldn't grow in that grassy and well-vegetated pasture as it's a weed of arable cultivation. In fact it's extremely rare in Yorkshire so would be exceedingly unlikely to be present in the area at all.