Distribution of Dimorphic Flowers as Related to Other Elements of the Reproductive Strategy

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Based on their functional role in reproduction, flower dimorphisms, whether structural or developmental, can be categorized as (1) pollination-related, (2) breeding-related, and (3) dispersal-related. Accordingly, flower dimorphism in Angiosperms is much more common than conceived before. For example, cleistogamy, considered a part of a multiple strategy in the breeding category, is found in over 200 species, 78% of which are herbaceous. It has haphazard systematic distribution and evolved in both zygomorphic (many Dicotyledones) and actinomorphic (many Monocots) flowers. The reproductive effort invested in the cleistogamous flowers proved to be by far smaller than in the chasmogamous ones. Thus cleistogamy has convergently evolved as an economical alternative mode of inbreeding in adverse conditions. Besides cleistogamy and its heteromorphic products, flower dimorphisms in general could be related to fruit dimorphism (heterocarpy) in some systematic groups. In the Tubuliflorae (Asteraceae) and the Apiaceae of Israel, heterocarpy is significantly more common among taxa with flower dimorphism. Flower and fruit dimorphisms represent a specialized or multiple reproductive strategy, with division of labour or alternative functions, in order to guarantee seed formation and dispersal even under stress.
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