My friend Carla Black is one of the most knowledgable and enthusiastic plant explorers and collectors I know. Her garden in Volcan, Panama would put many of the larger tropical botanical gardens to shame with her collections, mainly of Heliconias, but also with a large number of Costus. When I visited in 2008 there was a plant that had all the appearance of Costus laevis except it had the appendaged bracts and large stature of a Costus guanaiensis. She could not remember precisely where it was collected, somewhere in Panama.
The flower photos here are not very good and do not do justice to this plant, but I think you can get the idea. The real attraction here anyway is the foliage. This is a MASSIVE plant with very attractive purple-backed leaves, dark green on the upper surface with the silvery midstripe of C. laevis, and in this case it seems to stay intact at maturity unlike many C. laevis plants. If nothing else, it is worth something just to have one of this great lady's collections.
Carla has it growing in full sun in her garden and it succeeds there quite well despite the cooler temperatures of her location in Volcan. It probably would not withstand freezing temps or even heavy frost would severely damage the foliage, so I would not recommend outdoor growing colder than USDA zone 10.