Plant sexuality deals with the wide variety of sexual reproduction systems found across the plant kingdom. This article describes morphological aspects of sexual reproduction of plants. That plants employ many different strategies to engage in sexual reproduction was used, from just a structural perspective, by Carolus Linnaeus (1735 and 1753) to propose a system of classification of flowering plants. Later this subject received attention from Christian Konrad Sprengel (1793) who described plant sexuality as the "revealed secret of nature" and, for the first time, understood the biotic and abiotic interactions of the pollination process. Charles Darwin's theories of natural selection are based on his work. Flowers, the reproductive structures of angiosperms, are more varied than the equivalent structures of any other group of organisms, and flowering plants also have an unrivalled diversity of sexual systems. But sexuality and the significance of sexual reproductive strategies is no less important in all of the other plant groups. The breeding system is the single most important determinant of the mating structure of nonclonal plant populations. The mating structure in turn controls the amount and distribution of genetic variation, a central element in the evolutionary process.