Scytonema Agardh ex Bornet et Flahault

From Greek skytos, "leather" + nema, "thread" 
False branching begins to develop as both ends
of the filament break through the mucilage sheath.
The right portion has grown quite a bit, while the
portion to the left is just breaking through the sheath.
Scytonema filaments form dark mats or tufts amongst other algae or submerged vegetation in lakes or on terrestrial stones, wood, or soil. The trichomes are cylindrical and isopolar, and are usually colored pale blue-green, olive green, brownish, or even violet. The apical ends of the filaments are not tapered, but the end cells may slightly rounded or widened. The cells sometimes have constricted cross walls and contain groups of long, cylindrical gas vesicles. The heterocysts are located throughout the filaments and are rectangular and solitary, with darkly-pigmented cell walls. The trichomes are contained within mucilage that is commonly tough, wide, sometimes layered, and may be colored brown, yellow, or orange.
Double false branching often forms when a filament breaks apart at the site of a dead cell. Both ends of the filament then break through the mucilage sheath and continue to grow as "branches". Occasionally, false branching also forms at a heterocyst where the filament breaks apart in a similar manner.

Both pieces of the filament have grown extensively,
forming the characteristic false branching pattern.