Micrasterias sp. 200x magnification. Brightfield microscopy.

Micrasterias is an ornate alga that is a member of the order Demidiales. Desmids are unicellular (although some live in colonies/filaments) and they all have beautiful symmetry. As green algae, desmids are photosynthetic which means they convert light energy from the sun into chemical energy and release oxygen as a byproduct. Without phytoplankton like this green alga and Cyanobacteria doing this for the last couple billion years, our atmosphere wouldn’t be full of the ~21% oxygen needed to sustain animal life that we see today!

Although desmids are green algae and not land plants, they are charophyte algae which means they are members of the algal lineage most closely related to land plants and these two groups share a relatively recent (~500mya) common ancestor. In order to transition from mostly unicellular and completely aquatic, the ancestors of modern land plants had to have evolved to be desiccation(dryness)-tolerant and multicellular, with specialized cell types. It is no small feat to transition from protist to plant and some of the mechanisms that underpinned this transition include horizontal gene transfers from bacteria that lived in close association with charophyte algae and early plants, co-opting algal genes for new plant-friendly functions (a process called exaptation), novel gene origination such as through gene and genome duplication, the evolution of multiple plastids per cell, and others.