The question asks us to identify which group of organisms under the Kingdom Plantae are predominantly aquatic. Let`s dissect each option to determine the correct answer.

Option 1: Bryophytes - Bryophytes are a group of non-vascular plants that includes mosses, liverworts, and hornworts. While some species of bryophytes can be found in damp habitats like peatlands or along riverbanks, they are not predominantly aquatic.

Option 2: Algae - Algae are a diverse group of photosynthetic organisms that can be found in aquatic environments like oceans, lakes, and rivers. They come in various forms, including microscopic unicellular organisms and large multicellular seaweeds. Algae are predominantly aquatic, making them the correct answer to the question.

Option 3: Pteridophyta - Pteridophyta refers to ferns and their relatives, which are vascular plants that reproduce through spores. While ferns can thrive in moist habitats near water sources, they are not exclusively aquatic.

Option 4: Gymnosperms - Gymnosperms are plants that produce seeds but do not have flowers or fruits. Examples of gymnosperms include conifers like pine trees. Although some gymnosperms