Haplotaenium minutum

The genus Haplotaenium was erected only rather recently, as a taxonomic split off  from the genus Pleurotaenium*. Most striking differences between those genera are in the occurrence of a terminal vacuole (present in Pleurotaenium, absent in Haplotaenium), the configuration of the chloroplast (parietal in Pleurotaenium, axile in Haplotaenium**) and the morphology of the zygospore (smooth-walled in Pleurotaenium, provided with conical protuberances in Haplotaenium).

By far the best-known species of Haplotaenium is H. minutum (synonymous with  Pleurotaenium minutum). In the Netherlands it is of rather common occurrence in oligotrophic, acidic bog pools. Zygospores are only incidentally recorded but may be easily overlooked as the adhering, empty semicells are most readily detached.

** This difference is not absolute, for in the genus Haplotaenium transitions  between axile and parietal chloroplasts may be observed.

Image © Henk Schulp

Haplotaenium minutum. Notice the axile chloloroplast which is provided with some spiralling, longitudinal ridges and the absence of terminal vacuoles.

Cell dimensions (L x B): ca 140 x 15 µm

 

Reference:

* Bando, T., 1988. Haplotaenium, a new genus separated from Pleurotaenium (Desmidiaceae, Chlorophyta). Journal of Japanese Botany 63: 169-178.