The bracha on a mushroom is "shehakol" because the Talmud (Berachot 40b) correctly (I think) states that mushrooms do not derive their nutrients from the ground. If a mushroom is growing in a ...
I haven't studied Tractate Kilayim. I know you can't plant grapes with wheat. What about, say: Jazz apple = Royal Gala apple X Braeburn apple ? Nectarine = Peach X Plum ? Nectaplum = Nectarine X ...