Also called ‘Redsepal Evening-primrose’, this is our commonest evening-primrose. It is a tall and erect plant, densely covered in long hairs with red bases, and produces large yellow flowers formed of four petals. These flowers open just before sunset, as the name indicates, but they wilt by noon of the next day. It produces flowers every day for several weeks. The sepals are covered in red hairs, and the leaves are lance-shaped with crinkled edges.
It flowers June to September, and is found on waste and disturbed ground, railway embankments, roadsides, and coastal sand dunes. Introduced from North America, and common and widespread throughout except Scotland and Ireland where it is rare.