The phenomenon in which sexual reproduction requires the involvement of two different thalli. 
(from the article `fungus`) ...types, often designated + and (or and ). Gametes produced by one type of thallus are compatible only with gametes produced by the other type. ...
heterothallic, heterothallism Referring to algae and fungi, describing the condition in which there are two mating types that act as male and female, as opposed to one self-fertile individual.