Hapalosiphon Nägeli ex Bornet & Flahault (1886: 53)

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

Hapalosiphon Nägeli ex Bornet & Flahault (1886: 53)

Type: H. pumilus Kirchner ex Bornet & Flahault (1887: 61)

Filamentous thallose; thallus composed of irregular filamentous clusters, attached to the substratum, epiphytic on aquatic plants, or free floating in the metaphyton. Filaments irregularly arcuate, with uniseriate trichomes; with true, T-type branching, morphologically undifferentiated between the main and lateral trichomes, rarely with branches that are slightly narrower. Sheaths thin, colourless, rarely indistinctly layered. Heterocytes intercalary, uncommon in lateral branches. Vegetative cells cylindrical or barrel-shaped, distinctly constricted at the cross walls, sometimes with finely and sparsely granular contents. Heterocytes intercalary, cylindrical. Reproduction by hormogonia with aerotopes, separating from trichomes at the ends of lateral branches through the formation of necridic cells.

A cosmopolitan genus comprising 28 species; three are described here from freshwater habitats of north-eastern Australia. Most species grow in standing waters amongst aquatic macrophytes and in the metaphyton of littoral areas of lakes and lacustrine wetlands. Several species prefer moors and peaty waters, one species occurs in thermal waters, two species grow subaerophytically. Bibliography: Siva & Sant’Anna (1990), Hindák (2012), Komárek (2013), Komárek et al. (2014).

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- Cells of the main filament and branches usually of the same dimensions ..................................................................... H. hibernicus Cells of the main filament usually larger than the branches...............................................................................................................2 Filaments flexuous to irregularly coiled (6–) 8–20 μm wide............................................................................................. H. pumilus Filaments flexuous, 5.5–9.0 μm wide .......................................................................................................................... H. welwitschia