User:Johnleineweber/Herkogamy

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Herkogamy describes the spatial separation of anthers and stigma within hermaphroditic angiosperm flowers as a method of avoiding self-interference and promote outcrossing as the mode of reproduction. Self-interference may reduce viable seed set by clogging the stigma and reducing opportunities for pollen tube growth by more optimal candidate pollen grains. Hermaphroditic flowers face a conflict of needing to present two pollination surfaces, pollen and the stigma, in the same position to increase the efficiency of pollen transfer coupled with the need to avoid self-interference by these presented surfaces. The functional value of herkogamy in self-incompatible flower species is associated with male fitness by patterns of pollen transfer. The amount of herkogamy present on an individual flower, that is the degree of separation of male and female sex organs, may help classify the degree to which that individual may self-pollinate. Herkogamous species are biotically pollinated and therefore dependent on pollinators for reproductive success. Not to be confused with dichogamy which is the temporal separation of reproductive structures. In herkogamous flowers the stigma and anthers are active simultaneously.

Forms of Herkogamy

Ordered herkogamy describes pollen and stigma positioned along the pathway a visiting pollinator takes on approach of the flower, thus facilitating cross pollination.

Approach herkogamy is theorized to be evolutionarily derived from protandry. It is characterized by the shortening of staminal filaments so that anthers are placed below the stigma. The reorientation of anther position allows pollen to present outwards, and the narrowing of corolla tube thus narrows the path a pollinating insect may take to reach nectar and ensures contact with pollination surfaces. This ensures pollinators first contact the stigma before removing pollen from anthers.

Reverse herkogamy is theorized to be evolutionarily derived from gynodioecious species. It is characterized by stigma placement below the anthers. Floral visitors contact anthers before the stigma. It has been suggested to facilitate greater pollen export than approach herkogamy and is typically associated with lepidopteran pollination

Movement herkogamy - touch-sensitive stigma that close on contact - see also: thigmonastism. Study suggests that is ineffective at preventing self-fertilization and that, along with selection against anther-stigma separation in an environment without pollinators present, contributes to prevalence of autogamy

Reciprocal herkogamy - mechanical method of reducing selfing/sexual interference while increasing rate of precise transfer of compatible pollen across floral morphs. Darwin proposed heterostylous floral polymorphisms resulting from selective pressures favoring legitimate pollen transfer between anthers/stigmas located at same level.