Filamentous algae are composed of cells that divide along a single plane, allowing only elongation to form filaments of one or more rows of cells. Algae that can divide in two planes can form sheet-like thalli or bodies.
Cells within filamentous algae divide along a single plane, allowing for elongation and the formation of filaments with one or more rows of cells. Algae that can divide in two planes are able to produce sheet-like thalli or bodies.