in which seed release occurs in response to an environmental trigger, rather than spontaneously at seed maturation. The most common and best studied trigger is fire, and the term serotiny is used to refer to this specific case.

Possible triggers include:
* Death of the parent plant or branch (necriscence)
* Wetting (hygriscence)
* Warming by the sun (soliscence)
* Drying atmospheric conditions (xeriscence)
* Fire (pyriscence) - this is the most common and best studied case, and the