Step 1: Understanding the Concept:
Plant classification breaks down different groups based on body differentiation, the presence of vascular tissues, and seed production capability.
Step 2: Detailed Explanation:
Spirogyra is a genus of filamentous, unbranched green algae belonging to the class Chlorophyceae. It is characterized by its unique spiral or helical arrangement of chloroplasts within its cells. Like other thallophytes (algae), its body lacks true roots, stems, or leaves, and it grows primarily in freshwater environments.
Step 3: Final Answer:
Spirogyra belongs to the Algae group.