InDesign :: Index Entries From Figure Captions

In my document, all index entries will come from text located adjacent to an image, or on the facing page. I had planned to create a uniquely named character- or paragraph style for this purpose, and to import all items formatted in that style into the index topic list. Or is there some better method of tagging the captions?
 
Each figure caption consists of two parts: botanical name and source. If this design works, I propose to format the first part  to a unique paragraph or character style, and add that to the index.
 
if that is the best approach, or other approach, and how best to implement it.