What is the primary characteristic of filamentous algae?

Filamentous algae are primarily characterized by their growth in long, thin strands or filaments. This structure allows them to occupy various water environments and increases their surface area for photosynthesis. These strands can often be seen floating or moving with water currents, contributing to their distinctive appearance in aquatic ecosystems. Unlike solitary organisms, filamentous algae form colonies or mats, which can impact water quality and aquatic life through excessive growth, sometimes leading to problems like oxygen depletion. Thus, the characteristic of growing in long, thin strands is integral to identifying filamentous algae and understanding their ecological roles.