Well, that has a long history, too. Living beings are like that; even non-sapient ones will intentionally exterminate rivals given the chance.

"I noticed. It was rather refreshing to see." Well, to see a nice flower patch at all, really.

As for the flowers Merlin's brought forth, they're strictly ones he's familiar with. So varieties native to Earth, especially those from the region of the British Isles, with a few more unusual ones like those from Avalon, as well.