Conjugating Green Algae Including Desmids

Abstract

The conjugating green algae (Zygnematophyceae) are among the most widespread and commonly encountered green algae in freshwaters of North America. Common in the benthos and plankton in ponds, streams, and ephemeral streams and Sphagnum bogs and in some subaerial habitats, conjugating green algae occur in diverse epiphytic assemblages on mosses and aquatic plants. Some taxa are valuable as ecological indicators. Cell shapes range from oblong coccoids to cylindrical cells in long branched or unbranched filaments, as well as complex segmented cells with elaborate shapes and surface ornamentation. Plastids shapes are diverse, including globose, ribbonlike, and elaborately lobed forms. Vegetative reproduction and asexual spore formation is common. Cells lack flagella, and iso- or anisogametes fuse within tubes or vesicles. The zygote undergoes meiosis and produces from one to four haploid germlings. Genera are distinguished by morphology, although several are clearly polyphyletic and contain many cryptic taxa identifiable only through molecular genetic markers.