Terms Used in These Descriptions
Maas has a supplemental key in his Costus descriptions In Flora Neotropica Monograph No. 18, he calls Section I Costus, and Section II Ornithophilus. These are not hierarchial classifications, as there are Section I and Section II plants scattered in both Group 1 and Group 2 of his Key to the Species. Below is the definition and an example of each type.
Section I Costus
Labellum large, composed of a short, rather broad tube and a distinct, exposed limb, color white to yellow, lateral lobes often striped with red to purple, bracts mostly green. (species #8-18)
Section II Ornithophilus
Labellum small, tubular, yellow, orange or reddish colored, bracts of the same color or rarely green. Named such due to premise that hummingbirds pollinate the tubular flowers. (species #19-36)