Final answer:
Angiosperms, or flowering plants, first appeared about 125 million years ago and have become the dominant terrestrial plants. Comprising both monocotyledons and dicotyledons, they have evolved to be highly diverse with more than 300,000 species.
Step-by-step explanation:
Evolution of Angiosperms
The first true flowering plants, known as angiosperms, are believed to have evolved approximately 160 million years ago. However, the most definitive fossil evidence suggests that angiosperms appeared about 125 million years ago during the Lower Cretaceous period. These early flowering plants rapidly diversified by the Middle Cretaceous roughly 100 million years ago. The emergence of flowers and fruit represent an evolutionary advantage, providing protection for embryos, increasing genetic variability, and aiding in seed dispersal. Angiosperms, with more than 300,000 species, are now the dominant form of terrestrial plant life and represent a major component of most ecosystems.
Angiosperms are composed of two main groups, the monocotyledons and dicotyledons. Monocotyledons, or monocots, include plants such as grasses and lilies, characterized by seedlings with a single leaf. In contrast, dicotyledon seedlings, which include a vast array of flowering plants, typically have two leaves. Both have evolved complex relationships with pollinating insects, which contributed to their wide variety and successful colonization of diverse habitats.