The perspective is a little odd, yea but i've seen orthographic perspective mixed with straight down foliage before.
I don't remember ever seeing that, and it's not working here for me either. = \
I had no idea what your trees were! I read them as pits of slime, because they're so dark compared to the grass around them, and because there are no trunks.
I like the rest of your tiles, though. Reminds me a lot of the old Enix stuff, which has a very warm place in my heart. =)
The whole set is very coherent, too; it all looks like it really belongs together, which is great.
Keep up the good work!