Final answer:
True, seed plants are the most plentiful land plants in existence, representing over 90 percent of Earth's vegetation due to their evolutionary adaptations.
Step-by-step explanation:
True: Seed plants are indeed the most plentiful land plants today. Seed plants, or vascular plants, which are also known as tracheophytes, make up more than 90 percent of Earth's vegetation with about 260,000 species. These plants have successfully proliferated across a variety of habitats due to several evolutionary adaptations that allow them to overcome challenges faced by their seedless counterparts. For example, seed plants have developed strategies for more efficient water conservation and dispersion of reproductive cells, allowing them to thrive in areas ranging from arid environments to tropical forests.
Comparatively, seedless plants, including ferns with roughly 12,000 species and mosses, are now only a small fraction of Earth's plant life, predominantly found in moist and shaded areas. This is a stark shift from 300 million years ago during the Carboniferous period when seedless plants were the dominant forms of plant life. The advancement of seed plants, therefore, represents a significant shift in the composition of terrestrial biomes throughout Earth's history.