Reproductive systems of angiosperms vary greatly among species ( Box 1-1), but two processes are necessary for sexual reproduction in all angiosperms: pollination-the transfer of pollen from the anthers of a stamen to the stigma of a pistil-and fertilization-the fusion of the sperm nuclei from pollen with the egg nucleus in the ovary to produce an embryo. Moreover, angiosperms have enhanced aesthetic, recreational, and cultural pursuits since before recorded history. Humans derive food, fiber, drugs, and fuel, either directly or indirectly from angiosperms. At the base of most terrestrial and many aquatic food webs, the angiosperms are the principal providers of nutrients and resources to most other organisms, and they provide multidimensional structure for the majority of terrestrial and freshwater ecosystems. More than 250,000 species of flowering plants have been described, and an equivalent number could await discovery (Davies et al., 2004). ![]() The angiosperms-flowering plants that produce seeds often enclosed within an edible fruit-are among the planet’s most successful life forms.
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