The group of plants that is most successful would probably be Angiosperms! They're also known as flowering plants or anthophytes.
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C, population, is not a formal taxonomic category
The pelagic zone can be contrasted with the benthic and demersal zones at the bottom of the sea. The benthic zone is the ecological region at the very bottom of the sea. It includes the sediment surface and some subsurface layers. Marine organisms living in this zone, such as clams and crabs, are called benthos.