Stigonema sp. Agardh, 1824
The branching trichomes of Stigomena have a main axis that are partly or wholly multiseriats. Branches arise from all sides of the main axis and may be repeatedly branched. Or branches may be borne unilaterally and unbranched. The sheath is always distinct, with a smooth or rough texture, homogeneous or lamellated, and hyaline or coloured yellow-brown, brown or black. The cells are spherical, although in young filaments they may be flattened. Heterocysts exist along the main axis or along branches.
Stigonema grows on damp to wet rocks, walls and cliff surfaces. It is also found growing on moist earth as well as floating clumps mixed with other algae.
Bold, H. C., C. J. Alexopoulos & T. Delevoryas, 1987. Morphology of plants and fungi. Harper & Row, New York. (5th ed.). 912pp.