What characterizes an alga?

An alga is characterized by being a chlorophyll-containing plant that does not have true roots. This classification highlights the defining features of algae, which are primarily aquatic and capable of photosynthesis due to their chlorophyll content. Unlike vascular plants, which have complex structures including roots, stems, and leaves, algae may have simple structures that allow them to thrive in their aquatic environments. They can vary greatly in size and complexity, ranging from single-celled organisms to large seaweeds, but they all share the absence of true roots. This factor is essential in distinguishing them from more sophisticated vascular plants, which possess specialized structures for nutrient and water absorption, as well as support and reproduction.