Swertia
This genus is new to us, but its part of the Gentianaceae family (which includes the ever so beautiful Gentiana and Tripterospermum) which is a good start. Over 160 species grow through much of Europe and Asia, with smaller number in eastern Africa and western North America. Annuals or perennials, with opposite pairs of leaves. Flowers on a spike, 4, or 5-petalled. Try in a reasonable soil (not too dry) sun to part shade.
What a fascinating flower swertia is! Unlike most flowers that tuck their nectar away, requiring the pollinators to rummage and become drenched in pollen, in Swertia the nectar is produced in open patches in the middle of the petals, yellow/green in the case of S. bimaculata. It is believed this encourages pollinators, mostly honeybees and solitary bees, to circle within the flower, thus encouraging more regular pollination than in most 'open' generalist flowers.