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Let your character stumble upon the book of a monk, that analyzed the flower. I guess he tried to remove the flower from the cave, expose it to sunlight, try growing other flowers in the cave, etc....
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/30412 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
Let your character stumble upon the book of a monk, that analyzed the flower. I guess he tried to remove the flower from the cave, expose it to sunlight, try growing other flowers in the cave, etc. Then you can summarize the findings of that monk, leaving your character puzzling over what that implies. You can do that before or after your character finds the flower for himself. You can also introduce a series of books by that monk, on various different topics, allowing you to have a recurring way of explaining other strange things in your world.