Polemonium caeruleum Jacob's-ladder
This plant is a rarity in Britain although it does grow in quantity in places like Lathkil Dale in Derbyshire. It is also uncommon in Europe and classed as an alpine because it will grow at heights of up to 7,500 feet. It had been seen at such heights on other occasions by members of our group and so the seeds were presumably washed down by the river where they germinated on the bank at a mere 4,000 feet.