Thallus filamentous, spongy, soft tufts, anywhere from 5 - 50 cm in length. Branches mostly on one side, at times, strongly rebranched and claw-like, maximum number of branches at joints one to four, rarely five. Rhizoids fine, often connecting to adjacent filaments by hapteroid-like rhizoids.  C. vagabunda grows from 4 cm diameter on wave-swept habitats to 30 cm high in protected habitats.  Pale green to grass green.

Filament cells cylindrical, 80-140 µm diameter wide, 4-12 µm long; branchlets tapering to 40 µm diameter, slightly constricted at junction with main axes; apices straight above, curved or sickle-shaped below; apical cells 20-60 µm diameter wide, 5-11 µm long. Cell divison intercalary, not apical.

Cladophora vagabunda forms pompon-like tufts attached to coral, basalt substrate, and other hard surfaces on reef flats. This alga is found near zero tide level on protected rocky coastlines and in tidepools.

Cladophora vagabunda forms small, pompon-like tufts on hard substrates at the zero tide level on reef flats. The small tight clumps enable this alga to withstand high wave action and scouring, but the compact morphology also inhibits invasive tendencies of the opportunistic settler in normal environmental conditions. This small green alga is usually only a small part of the biomass of the diverse, highly competitive intertidal community. By virtue of its dense and self-shading form, the alga rarely experiences photo inhibition except in the branches on the very top of the tuft, and thus tends to attach to solid substrate areas that are quite exposed. The alga has, however, demonstrated nitrate storage capabilities which increase its longevity in stressful conditions.

All of the Cladophora species are opportunistic settlers that respond to environmental variation. Nutrient loading, water temperature fluctuations, and downwelling illumination all influence the growth rates and longevity of these alga. In areas of eutrophication, opportunistic species like C. vagabunda may play an important role in coral reel community shifts.