Desmid of the month
destitute of any cell wall ornamentation, Cosmarium ralfsii,
in particular the variety montanum, can be readily distinguished
by its large cell dimensions and characteristic shape. C. ralfsii var. montanum differs from the nominate variety in that the
basal semicell angles are somewhat produced (giving the impression
of being slightly tipped up).
the Netherlands C. ralfsii is very rare and indicative of
acidic, oligotrophic habitats where there is a slight input of minerals
from the subsoil or the surroundings. It goes as an ecologically
most demanding species, indicating a high conservation value.
Image © Koos Meesters
ralfsii var. montanum as recently sampled from a Dutch
moorland hollow. Notice the produced basal angles of the semicells.
dimensions (L x B): ca 110 x 100 µm