What determines the flowers found on nook mile islands?

[mystery]

Do they always stick to the same two types or can they change at all by season? Hybrid islands are special as they can make rare flowers like blue roses or purple hyacinths easier than normal so I’m hoping one day I’ll have a chance at more.

 

[skogkyst]

I'm fairly certain that they work like fruits, in that most of them are one type but there's a small chance for the "rare" type. For me, those are pansies and windflowers.