Seed heteromorphism and plant life cycle: a review of literature

The species which produce two or more seed types represent groups where divergent strategies usually existing in different taxa are combined by one individual. In such groups, there is a tendency for seed functions to diverge, each type specializing on some aspect of environmental variation to which it is predisposed while being buffered by the other seed type. Two main types of this behaviour are distinguished, i.e. heterodiaspory and amphicarpy, based on the morphology of diaspores, their spatial distribution on a plant, dispersibility, and other ecological functions. Ecology of heterodiasporic and amphicarpic plants is reviewed in relation to particular life cycle stages and habitat conditions. It is concluded that seed heteromorphism represents a) a form of bet-hedging in the face of temporal variation in environmental suitability in habitats where changes of environmental conditions from season to season and year to year are very frequent and no single pattern of ecological behaviourcan ensure successful survival, b) escape from negative effects of densityor c) sib competition and occurs because intermediate adaptation have lowfitness.