Ice algae terrestrial ice algae occur in freshwater systems, the species composition differs greatly from that of sea ice algae. These communities are significant in that they often change the color of glaciers and ice sheets, impacting the reflectivity of the ice itself. Microbial life in sea ice is extremely diverse, and includes abundant algae, bacteria and protozoa. Algae in particular dominate the sympagic environment, with estimates of more than 1000 unicellular eukaryotes found to associate with sea ice in the Arctic. Species composition and diversity vary based on location, ice type, and irradiance. In general, pennate diatoms such as "Nitschia frigida"
Algae their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., "Chlorochytrium"), but later were seen as endophytic algae. Some filamentous bacteria (e.g., "Beggiatoa") were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae. The first land plants probably evolved from shallow freshwater charophyte algae much like "Chara" almost 500 million years ago. These probably had an isomorphic alternation of generations and were probably filamentous. Fossils of isolated land plant spores suggest land