Zygnema

Zygnema is a genus of filamentous green algae belonging to the order Zygnematales. These algae are characterized by their cylindrical cells arranged end-to-end, forming unbranched filaments. A distinctive feature of Zygnema is the presence of two large, spiral chloroplasts within each cell, which are crucial for photosynthesis. The spiral nature of these chloroplasts is a key diagnostic feature for identifying the genus.

Zygnema species are commonly found in freshwater environments, including ponds, lakes, ditches, and slow-moving streams. They can be epiphytic, growing on other aquatic plants, or free-floating in the water column. Reproduction in Zygnema can be asexual, typically through fragmentation of the filament, or sexual, via conjugation. During conjugation, two filaments come into close contact, and specialized structures called conjugation tubes form between adjacent cells. Gametes then migrate through these tubes to fuse, forming a zygote which develops into a zygospore. The zygospore is a resistant structure that can survive unfavorable conditions. Zygnema plays a role in aquatic ecosystems as a primary producer and a food source for various aquatic organisms.