This grower is fairly sure of this plant identification.
small very dark purple almost black flowers. Good for rockery.
Roscoea genus. There are about 18 species of tuberous perennials which are grown for their orchid-like flowers, wide-lobed lower lips and 2 narrower petals. The leaves are lance-shaped and upright.
They are frost hardy and will grow in the sun or partial shade in cool, humus-rich soil that should always be kept moist in the summer. Dies down in winter, when a top dressing of leaf mould or well-rotted compost is beneficial.
Grown for their orchid-like flowers. It is suited to open borders, rock gardens and woodland gardens.