Habitat comparison — Relative to green algae (Chlorophyta), how common are brown algae (Phaeophyta) in freshwater environments?

Introduction / Context:
Ecological distribution differs sharply among algal divisions. Brown algae (Phaeophyta) are largely marine macroalgae, whereas green algae (Chlorophyta) thrive in freshwater and a wide range of terrestrial and marine microhabitats.

Given Data / Assumptions:

• Phaeophyta (e.g., kelps, rockweeds) occur predominantly in marine environments.
• Chlorophyta include many freshwater lineages (filamentous, unicellular, and colonial forms).
• We compare relative numbers in freshwater.

Concept / Approach:
Because freshwater brown algae are rare and specialized, while freshwater green algae are abundant and diverse, the number of freshwater Phaeophyta members is less than that of freshwater Chlorophyta. Hence, “less common than freshwater Chlorophyta” is correct.

Step-by-Step Solution:

Verification / Alternative check:
Field guides list numerous freshwater green genera (e.g., Spirogyra, Chlorella), while freshwater brown algae are comparatively scarce.

Why Other Options Are Wrong:

• (a) and (c) contradict observed distributions.
• (d) is non-informative and unnecessary.

Common Pitfalls:
Assuming all macroalgae occur equally in all waters; salinity preferences are key.

Final Answer:
less common than freshwater Chlorophyta