CALYX: the outer whorl of floral envelopes, the sepals of one flower collectively.
The shape and length of the calyx in Costus is sometimes used to distinguish between species. Most Costus calyx are tubular and have three lobes either triangular or deltoid in shape. In some Costus species the calyx is deeply split along one side and in some there are two sharp keels, much like the bicarinate bracteoles. The Costus Identifier Tool includes the length of the calyx as an identifying characteristic. Measure from the junction with the ovary to the end of the lobes. I have used 10 mm (1 cm) as the dividing line between a long and short calyx.
Costus species with the calyx always longer than 10 mm are marked "Y". Costus species with the calyx always shorter than 10 mm are marked "N". If this characteristic is unknown, or if the calyx length can be either longer or shorter than 10 mm, it is entered in the GingersRus Plant Database as "U".

EXAMPLES OF COSTUS CALYX - These are pictures of Costus calyx attached to the ovaries, showing long and short, tubular or bicarinate.
Examples of Costus calyx