If the mysterious symbol resembles a comet, and a drop of sunlight is what caused the sunflower to grow....what might cause a moonflower to grow that also falls from the sky? Maybe a chunk of the comet broke off and became a meteor? Just sayin' XD
Okay, I’m gonna reel you back a moment and remind you not to think so literally. Sunlight does not literally come in drops. Therefore, you can be as fanciful as you want when it comes to something like this.
But let’s also look at it like this: in the concept, the moon is the opposite of the sun. The sun grants life. A drop of sunlight would be not unlike rain, which is also a lifegiver. If the moon takes life away, what could be used to represent that?
Moondust, for example. It’s a real thing, but it can’t fall from the sky (in reality), and might call to mind grave dust. I imagine it would resemble pixie dust as it falls, but maybe, even as the moonflower grows, it pulls the nourishment out of the surrounding soil.