Table 1 Diacritical morphological characteristics of four Aphanizomenon taxa reviewed from natural samples collected in the Nakdong River

Aphanizomenon flos-aquae

Band-like, up to 2 cm long, straight or bent, often grouped in fascicles

Elongated cylindrical, not narrowed, without aerotopes, almost hyaline

Cylindrical to slightly barrel-shaped, 4.0–12.1 × 3.6–5.6 μm^a (n = 45)

Intercalary, solitary, cylindrical, 6.6–8.5 × 3.3–3.9 μm^a (n = 19)

Intercalary, long cylindrical, distant from heterocytes, 30–62 × 5.2–7.5 μm^a (n = 22)

Aphanizomenon klebahnii

Spindle-like, up to 3 mm long, straight or slightly arcuated, often grouped in fascicles

Elongated cylindrical, without aerotopes, and with remaining cytoplasm in the form of fine granulation

Cylindrical or slightly barrel-shaped, 3.9–8.3 × 3.6–4.9 μm^a (n = 31)

Solitary, intercalary, oval to cylindrical, 5.5–6.7 × 3.2–4.0 μm^a (n = 6)

Intercalary, solitary, elongated cylindrical, 26–39 × 4.5–5.9 μm^a (n = 17)

Aphanizomenon skujae

Solitary, straight, bent or irregularly curved

Narrowed and elongated, bluntly pointed, containing a smaller amount of pigment and sporadic aerotopes

4.8–8.4 × 1.2–2.5 μm^a (n = 19)

Solitary, intercalary, oval to cylindrical, 6–15 × 2–3 μm^b

Solitary or up to 3 in a row, cylindrical with rounded ends, wider than trichomes, 7.6–11.8 × 3.8–4.6 μm^a (n = 13)

Cuspidothrix issatschenkoi

Solitary, straight, bent, or slightly coiled

Tapered like hair-shaped, almost hyaline, continually pointed

Cylindrical to long-cylindrical, usually with scarce aerotopes, 4.4–7.0 × 2.5–3.3 μm^a (n = 36)

Solitary, intercalary, 6.6–8.7 × 3.4–3.7 μm^a (n = 5)

Solitary or 2–3 in a row, distant from heterocytes, long cylindrical with rounded ends, 8.5–12.5 × 4–4.6 μm^c