[thaumasiotes]

> Potatoes and Tomatoes are very similar plants. You can graft them together and have a living plant that grows tomatoes on top and potatoes in the roots.

It's true that they're similar plants, but that's not a requirement of grafting.

[Jedd]

It kind of is, though.

Grafting specimens of the same species is fairly easy - grafting onto a different species but staying in the same genus is a little less reliable but the basis of most grafted orchard trees.

Grafting to a different genus, but within the same family, is much more challenging. Not impossible, of course, but less likely to succeed, so less commonly done.