Final answer:
True, red algae, green algae, and plants are closely related and are included in the Archaeplastida supergroup.
Step-by-step explanation:
The statement that red algae, green algae, and plants are so closely related that they are grouped in the same supergroup by most biologists is True. The Archaeplastida supergroup includes green algae (Chlorophyta and Charophyta), red algae (Rhodophyta), and land plants. Specifically, Charophytes are the closest living relatives to land plants and share many characteristics, such as the presence of chlorophyll a and b, cellulose cell walls, and the storage of carbohydrates as starch.
While Chlorophytes, also a subdivision of green algae, exhibit similar features and are sometimes even considered as part of the plant kingdom themselves, the distinction still remains due to differences in multicellularity and habitat, among other factors. Understanding the precise phylogenetic relationships between these organisms is critical for the study of plant evolution and biology.