Nostoc (Nostocaceae)

Diagnostic features

Chains of spherical cells packed together in rounded masses of firm mucilage attached to surfaces. Density of filaments within the colony varies according to growth conditions.  Organelles are absent from the cells, but granules or vesicles may be present, especially in older material. Heterocytes, which are typically larger and thicker walled, are occasionally interspersed between the standard photosynthetic cells.  The colony may be green, blue-green, purple, pink or yellow-brown.

Typical habitats

Most abundant in good quality stony streams/rivers

Classification