I have gotten one rare seed. It appears that the graphic shown as the seeds fly over to you is a random choice. When I saw an animation that looked like a rare seed, I got all commons as the reward, but when I got a rare seed in my assortment the animation was something common, a lemon maranta seed I think. It's also possible in my case that the seed that looked uncommon in "flight" was actually a lime daffodil seed. They can look odd in certain circumstances, none of which I remember now. The supposedly rare seed I saw in the animation was pinkish and roundish and I could be convinced it was a lime daffy seed.