Thionins are a family of small proteins found solely in higher plants.

The gamma thionins have a superficially similar structure but are an unrelated class of protein, now called plant defensins.

[2] The hydrophobic protein crambin from the Abyssinian kale (Crambe abyssinica) is also a member of the thionin family.

[1] Some thionins have cytotoxic activity and they are therefore interesting in the development of new drugs against cancer with novel action mechanisms.

Thionin is also a minor protein found in mustard (Brassica napus L.) seeds.