Papenfussiella callitricha (Rosenv.) Kylin, of the Myriogloia group (Chordariaceae), is an endemic species of west Greenland with a very restricted distribution; it is known from only 3 localities. The collections from which my own description of the plant is taken constitute the first records of the species since Rosenvinge's original collections of 1886. My cytological data are taken from living plants and ecological notes are based upon observations made while I dived with the aid of Scuba equipment. Zoospores liberated in culture medium germinated to produce microthalli, the second microthallus to be described for this algal group. The life history was not completed in culture. However, motile cells released from the plurilocular sporangia of the microthalli continued to produce more microthalli. I suspect that under natural conditions, the microthalli remain vegetative at the close of the daylight season, to resume reproduction late the following spring, giving rise to the next generation of macrothalli.