Dolichospermum

Taxonomy

Order Nostocales
Family Aphanizomenonaceae
Genus Dolichospermum

Morphology

Trichomes mostly solitary, though some commonly-occurring species tend to form entangled clusters/colonies. Trichomes are straight, curved, or coiled; isopolar; not narrowed towards the ends; usually with clear constrictions at crosswalls; metameric. Never with firm sheaths; sometimes with fine mucilaginous envelopes. Cells spherical, barrel-shaped, or nearly cylindrical; usually isodiametric, sometimes longer than wide (up to 2x longer than wide). Terminal cells not different from other vegetative cells; rounded at the ends. Obligately with aerotopes.

Heterocytes intercalary (but can be found in a terminal position only after disintegration of a trichome); solitary; usually spherical, sometimes barrel-shaped; as wide as vegetative cells (or nearly so; slightly wider or narrower). Akinetes intercalary; solitary, or sometimes in rows of up to 5; cylindrical, ovoid, oval, or spherical in shape; developing paraheterocytically, adjacent to or slightly distant from heterocytes.

Ecology

Trichomes are planktic, or rarely metaphytic. Mostly reported in temperate zones, in freshwater mesotrophic lakes and ponds. Capable of forming surface blooms.

Note that Dolichospermum was formerly classified as a cluster of "planktic Anabaena" species; the two genera are distinct phylogenetically, morphologically, and ecologically. Unlike Anabaena, Dolichospermum is planktic, cells obligately contain aerotopes, and trichomes are mostly solitary (not forming mats).

References

Johansen, J. R., & Komárek, J. (2015). Filamentous Cyanobacteria. In J. D. Wehr, R. G. Sheath, & J. P. Kociolek (Eds.), Freshwater Algae of North America: Ecology and Classification (2nd ed., pp. 183-214). Waltham, MA: Elsevier.

Komárek, J. (2013). Cyanoprokaryota-3. Teil/Part 3: Heterocytous Genera (J. R. Johansen, Ed.). In B. Büdel, G. Gärtner, L. Krienitz, & M. Schagerl (Eds.), Süßwasserflora von Mitteleuropa (Vol. 19/3, pp. 697-698). Heidelberg, Germany: Springer Spektrum.

Strunecký, O., Ivanova, A.P., & Mareš, J. (2023). An updated classification of cyanobacterial orders and families based on phylogenomic and polyphasic analysis. Journal of Phycology, 59: 12-51. https://doi.org/10.1111/jpy.13304