Flowers are what actually makes angiosperms different from other seed plants. They serve as their reproductive structure and allow them to form a broad range of evolutionary relationships. You know what else is cool? Their stamens prevent them from performing self-fertilization which broadens the niches they effect.
The fact that angiosperms lay seeds sooner and faster than gymnosperms makes it hard for me to believe that these flowering plants aren't everywhere. In a way, however, they kind of are everywhere: they dominate terrestrial ecosystems, they are the most diverse and numerous land plant, and they are the most commercially significant plant to humans.
So with that I leave you with one final thought:
Watch out gymnosperms... here come the angiosperms!