With regards to this question about identifying a plant found in a garden in south India wich only flowers after rain, I'm planning to ask in a separate question why it does that.
Will that be on-topic?
Is it better to ask it in Biology SE?
I think it will depend on the type of answer you expect. Our help center has this text in the "don't ask" section:
plant biology, beyond what is generally gardening knowledge (try Biology instead)
So if you're just looking for the environmental trigger that causes the plant to flower after rain, that would be on-topic here. If you're looking for the environmental trigger and how that trigger causes changes in the biochemistry of the plant and how those changes eventually lead to flowering, then that would belong on Biology Stack Exchange.
An analogy would be the concept of forcing, using an artificial environment to satisfy a plant's requirements at specific points in its growth cycle. An example is chilling bulbs so as to have flowering Hyacinth or Narcissus at Christmastime. A biologist might know exactly what's happening internally in the bulb, but as a gardener I just need to know when to put the bulbs in the refrigerator and how long to keep them there.