Nostoc commune Vaucher
Desikachary 1959, p. 387, plate 68, fig. 3; Geitler 1930-32, p 845, fig. 536-37.

Mature colony upright spheres, bumpy, very cohesive, dark blue-green when observed at low power. When examined under a compound microscope, two colony forms were observed. Small, oblong colonies with a single series of cells, a thick, firm sheath, and an terminal external heterocyst. Trichomes from these colonies non-motile, highly constricted at the cross walls, not tapering, 5.6-8.0 m m wide. Cells granular, ellipsoid, shorter than broad, 4.8-5.6 m m long. Heterocysts hemispherical, terminal, often outside of the sheath material, 3.2-7.2 m m wide, 4.8-5.6 m m long. Akinetes undetected, but it is possible that some of the larger cells in the small colonies were in the process of akinete formation. Large spherical colonies with several distinct trichomes in a soft diffluent mucilage. Trichomes from these colonies non-motile, constricted at the cross walls, not tapering, 3.2-5.6 m m wide. Cells not granular, ellipsoid, often longer than broad, 3.2-7.0 m m long. Heterocysts spherical to subspherical, always within the sheath material, often separated from trichomes, 3.0-6.0 m m at widest diameter. Akinetes in large colonies spherical, 8.0 m m in diameter. Hormogonia lacking sheath material, short (3-20 cells long), motile, highly constricted at the cross walls, not tapered, 2.8-3.2 m m wide. Hormogonial end cell slightly larger and longer, up to 4.0 m m long, not very differentiated. Hormogonial cells finely granulate, compressed globose to barrel shaped, 2.4-3.2 m m long. Heterocysts absent in hormogonia.

This species is highly variable through time, due to the various life-cycle stages. Large spherical colonies release narrow hormogonia, which grown into the small oblong colonies (known as the punctiform stage), which mature into the larger spherical colonies. This taxon is very similar to N. punctiforme, which we identify as often not producing the larger colonies, and producing hormogonia more profusely.

CNP 1, plate Z1, c 13 (roll 8-2 e. 12,13, 14)
CNP 3, plate B1, c 6 (e. 29, 30) (roll 12-2, e. 3)
SEV 2, plate 1, c 2 sp. 1 (exp29 100x)
SEV 5, plate 4, c 5 (e. 30, (31-20x))
SEV 3, plate 1, c 7 tiny dark green ball
SEV 4, plate 4, c 10 sp. 2 (e. 19) colony contaminated with fungus
SEV 4, plate 4, c 6 sp. 2 (e. 13,14) (roll 10-2 e. 27, 28, 29) large mound of small balls
SEV 3, plate 5, c 6 (e. 26) No isolate small short individual colonies, very distinct
SEV 3, plate 5, c 4 dark green small individual colonies