Which of the following plants are the smallest of all green plants that can grow in soil, on trees, and on the bodies of turtles and frogs?

The correct choice identifies algae, specifically noting that they are among the smallest of green plants capable of growing in a variety of environments, including soil, on trees, and even on the bodies of animals like turtles and frogs. Algae are predominantly aquatic organisms, found in both freshwater and marine environments. They can thrive in various habitats because some types are adaptable to moist terrestrial conditions as well.

While algae are key photosynthetic organisms, it is important to understand that they can form a resilient part of ecosystems, contributing to nutrient cycling and serving as a food source for various aquatic life forms. Their cellular structures and growing conditions also make them uniquely capable of colonizing different surfaces, including living organisms.

In contrast, mosses are small non-vascular plants that typically grow in moist locations but do not have the ability to grow on animals. Lichens, a symbiotic association of fungi and algae, can inhabit a variety of surfaces but don't typically fall into the category of 'green plants' in the same way algae do. Sago palms, being large and only found in specific environments, do not fit the criteria of being small or able to grow on diverse surfaces such as those listed.