Diagnostic features
Tapering, sheathed heteropolar filaments attached to surfaces. Spherical or near-spherical heterocyte always occurs at the base of each filament. Basal cells often widened. Tufts formed by groups of filaments often trap sediment near the base. Filaments within groups are separated from each other (not in common mucilage), and false branching very rare to absent (cf. Dichothrix).
![[Calothrix], Kakanui River, X20. Photo: Otago Regional Council & Manaaki Whenua Image](/assets/Tools-And-Resources/Identification/algae/calothrix20__ScaleWidthWzEwMjRd.jpg)
![[Calothrix], Kakanui River, X160. Photo: Otago Regional Council & Manaaki Whenua Image](/assets/Tools-And-Resources/Identification/algae/calothrix2__ScaleWidthWzEwMjRd.jpg)