My landlord has this plant in his garden. (See pictures at the bottom.) I water it for him several times a week, using water from a closed well.
It doesn't usually rain here. There's maybe one or two periods of rain each year. The rest of the year we have a dry, tropical climate.
No matter how much I water it, this plant never flowers. I've tried copious amounts of water, frequent watering, etc. It doesn't matter.
However, when it rains, like it did this week, it only takes a few days for the plant to give these beautiful flowers. As far as I have seen, this rule never fails. The plant never flowers after being watered with well-water, but always flowers after rains.
What is the name of this plant?
We are in southern India. The plant may be native to this area, it might be native to somewhere else. I'm not sure. But it does fine here, except for the well-water thing.
As for why it only flowers after rain, that is not the purpose of this question, but people are welcome to mention that. I intend to ask it in a sepreate question once I have ascertained the name of the plant.
With a DVD for size comparison: