Calothrix C.Agardh ex Bornet & Flahault (1886: 345)

Mcgregor, Glenn B., 2018, Freshwater Cyanobacteria of North-Eastern Australia: 3. Nostocales, Phytotaxa 359 (1), pp. 448-450 : 448-450

Calothrix C.Agardh ex Bornet & Flahault (1886: 345)

Type: C. confervicola C.Agardh ex Bornet & Flahault (1886: 349)

Filaments heteropolar, clearly differentiated into basal and apical parts, simple, solitary or in small groups, separated from one another, rarely occurring solitary, lateral false branches, generally oriented in the direction of the original growth. Trichomes with basal, spherical or hemispherical heterocytes, occasionally forming intercalary cylindrical heterocytes. Trichomes sometimes with widened basal parts, constricted or unconstricted at the cross walls, ending in a hair-like apical region composed from narrow, long, hyaline cells. Sheaths always present, usually firm, sometimes lamellated and yellow-brownish in colour or funnel-shaped widened at the ends. Vegetative cells cylindrical or barrel-shaped, aerotopes absent. Akinetes rarely in basal parts, however this has been reported in a few species. Cell division occurs perpendicularly to the long axis of trichomes. Trichomes dissociate at heterocytes and separately develop into new trichomes. Reproduction by motile hormogonia, which divide from the trichome, by the formation of necridic cells and liberate from the sheath after separation of the terminal hair; hormogonia of several species produce aerotopes.

As currently prescribed, the genus Calothrix is polyphyletic. Several genera, that are morphologically similar, and can only be confidently distinguished on molecular criteria, have been recently separated ( Calochaete Hauer et al. , Roholtiella Bohunická et al. , Macrochaete Berrendero Gómez et al.); other future revisions are likely. Many Calothrix morphotypes were observed in collections from a variety of habitats throughout north-eastern Australia, however most were not able to be identified based soley on morphological criteria. Due to the uncertainty about the genus, four morphotypes have been given nominal designation here. Bibliography: Berrendero et al. (2008), Hauer et al. (2013), Komárek (2013), Komárek et al. (2014), Bohunická et al. (2015), Berrendero Gómez et al. (2016).

1.

-

2.

-

3.

-

4.

-

5.

-

6.

-

Mature trichomes tapering to fine, hair-like cells which are often hyaline........................................................................................2 Mature trichomes do not taper to fine, hair-like cells.........................................................................................................................3 Sheath lamellated, often funnel-like widened, colourless to yellow-brown in colour. ..................................................... C. cf. fusca Sheath fine, hyaline, colourless............................................................................................................................................... C. sp. B Vegetative cells pinkish-red to violet in colour .................................................................................................................. C. atrichia Vegetative cells blue-green to olive in colour....................................................................................................................................4 Trichomes cylindrical, not or slightly tapered towards the ends.................................................................................... C. brevissima Trichomes clearly tapered towards the ends.......................................................................................................................................5 Basal heterocytes 3.0–5.5 μm broad ....................................................................................................................................... C. sp. C Basal heterocytes> 10 μm broad.......................................................................................................................................................6 Filaments typically solitary, up to 220 μm long, vegetative cells 2.2–6.0 μm long × 7.5–14.5 μm broad............................. C. sp. A Filaments many together forming a dense erect turf, up to 2 mm in length, vegetative cells 3.5–4.6 μm long × 11.2–13.5 μm broad........................................................................................................................................................................................ C. sp. D