Tweet this page Like this page Email this page Share this page Home» Resources » Identification » Identification of algae » Freshwater algae » How to identify algae » Identification guide » Filamentous » Filaments microscopic » Filaments are unbranched Filaments are unbranched 4. Please select the filament colour. Blue-green, grey, whitish or reddish - no organelles Chloroplasts visible inside cells are green or yellow-green Chloroplasts visible inside cells are brown; cells are box-like and may be semi-rectangular (visible when filament bends) - chain-forming diatoms