TABLE 2.

Cyanobacterial morphotypes distinguished in the four crusts

Morphotype (main characteristics)	Assignment per Geitler (19)	Abundancea in
		Sandy soil	Shale	Gypsum	Silt
Ensheathed, bundle-forming filaments, nonheterocystous; trichomes 4–6 μm wide; no constrictions at cross-walls; cells quadratic, 5–7 μm long; necridia present; apical cells with calyptra	M. vaginatus (Gomont)	++++	++	−	++++
Ensheathed, bundle-forming filaments, nonheterocystous; trichomes 2.5–5 μm wide; cells 2.5–4 μm wide; slightly constricted at cross-walls; apical cells conical; sheath colorless or with scytonemin	Schizothrix spp.	++	++	+	++
Single filaments, nonheterocystous; trichomes 1.2–2.5 μm wide; barrel-shaped, isodiametric cells; round apical cells	Phormidium spp.	+	−	++	+
Heterocystous filamentous; lamellated, brown sheath; filaments 10–15 μm wide; trichomes 8–11 μm wide; cells disc-shaped, 3–5 μm wide; terminal and intercalary heterocysts	Scytonema sp.	+	++	++	++
Heterocystous filamentous; short chains of spherical cells, 3.5–5 μm in diam; confluent gel holds trichome masses in spherical dark-brown colonies 90–500 μm in diam	Nostoc sp.	−	−	+++	+++
Heterocystous, disorderly masses of cells forming spherical colonies with tight, clored sheaths; upon cultivation, filaments with true branching formed; cells 3.5–7 μm wide	Chlorogloeopsis sp.	−	−	−	+

^a++++, dominant; +++, very common; ++, common; +, present; −, not detected.