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.