Cuckoo flower, also known as Lady's Smock has pretty lilac flowers and grows in wet meadows and on riverbanks and roadside verges.
The flowers emerge at the same time as the cuckoo begins to sing, hence its name.
A frothy/foamy substance known as 'cuckoo spit' sometimes appears on cuckooflower. This 'spit' is actually the larvae of the Froghopper, which protects it from predators.
There's a lot of it around Otley at the moment: these photos were taken by the stream at Otley Golf Course and in a local garden.