SAR supergroup

Many tiny living things are in one big group.

This group is called SAR. It has three parts. One part has tiny hairs.

Another part has small sacs under its skin. The third part is called rhizarians. Some of these things live in the sea. Some can make their own food from light. Others do not make food this way. Some are very small. Others grow into big seaweed forests.

This group is very large. It is half of all tiny life!

Scientists found a very large group of life. They call this group SAR. The name comes from three parts. These parts are stramenopiles, alveolates, and rhizarians.

This group is very diverse. Some members are tiny. Others grow into big kelp forests. Some make food from light. Others do not. Some even use light in different ways.

Stramenopiles have tiny hairs. These hairs are called mastigonemes. Alveolates have small sacs under their skin. We call these sacs alveoli.

Scientists found this group by studying genes. This is called phylogenomics. It is a way to look at the building blocks of life. This helped show how these three parts are related. Some think a group called telonemids is a close relative. This would make a larger group called TSAR. SAR is huge. It may include half of all tiny life on Earth.

Scientists have found a massive group of life called SAR. This name is an acronym. It uses the first letters of three main parts. These parts are stramenopiles, alveolates, and rhizarians.

This group is very important to our world. It includes many different kinds of living things. Some experts think it may hold half of all eukaryotic life. These are living things with complex cells.

How this group works is quite interesting. The members have many different shapes and ways of living. Some are tiny bits of life in the water. Others grow into huge kelp forests. Some members use photosynthesis to make food from light. They do this by using parts from red algae. Other members, like some rhizarians, use parts from green algae.

They even keep tiny leftover parts from these old cells.

We did not always know about this group. Before, scientists put stramenopiles and alveolates in a group called Chromalveolata. They thought they all shared a common ancestor. They also thought Rhizaria was a separate group. Later studies changed this view. Scientists used a method called phylogenomics to look at genes. This showed that these three groups belong together.

There are many specific facts about these living things. Stramenopiles have a special hair on their front. These hairs are called mastigonemes. Alveolates are different because of their cortical alveoli. These are small sacs under their outer layer. Some scientists study a group called telonemids. Telonemids might be a close relative to SAR. This would make a larger group called TSAR.

You can see how this links to nature. Think about the huge kelp forests in the ocean. Those forests are part of the SAR group. You might also see tiny life in a pond. Many of those tiny things are also in SAR. It is a huge part of the tree of life. This group helps us understand how life branched out.

The SAR supergroup is a massive and diverse collection of eukaryotic life. Eukaryotes are organisms with complex cells. The name SAR is an acronym. It comes from the first letters of its three main parts: stramenopiles, alveolates, and rhizarians. This group is a node-based taxon. This means it includes all descendants of a specific last common ancestor. Scientists consider this group very important because it is so large. It is estimated that SAR might encompass up to half of all eukaryotic diversity on Earth.

Members of the SAR group show incredible variety in their shapes and lifestyles. Some organisms are microscopic phytoplankton that float in the ocean. Others are massive kelp forests that grow underwater. The group includes both photosynthetic and non-photosynthetic forms. Photosynthesis is the process of using light to make food. Many stramenopiles and alveolates gained the ability to photosynthesize through secondary endosymbiosis. This is when one cell captures another cell to gain a new function. In these cases, they acquired plastids, or light-catching parts, from red algae.

Rhizarians show a different way of obtaining energy. Some chlorarachniophyte rhizarians captured plastids from green algae instead of red algae. These cells even retain vestigial nucleomorphs. A nucleomorph is a tiny, leftover nucleus from the original captured cell. This shows that different groups within SAR can follow different evolutionary paths. While they share an ancestor, their ways of getting food vary greatly. This diversity makes the SAR supergroup a central part of biological studies.

We did not always know about the SAR supergroup. In the past, scientists used a different classification system. They placed stramenopiles and alveolates into a group called Chromalveolata. This group also included haptophytes and cryptomonads. Scientists once believed all these organisms shared a common ancestor through red algal endosymbiosis. They also believed rhizarians were a completely separate supergroup. However, modern research changed these ideas.

Newer studies used a method called phylogenomics to study the relationships between life forms. Phylogenomics uses genetic data to build maps of how species are related. These studies confirmed that stramenopiles and alveolates diverged alongside rhizarians. This proved they belong to the same SAR lineage. This discovery excluded haptophytes and cryptomonads from the group. Scientists now propose a different group called Hacrobia for those organisms. This is because haptophytes and cryptomonads likely acquired their plastids through separate events.

Because SAR was discovered through genetic studies, it lacks a single physical trait that unites every member. In biology, these shared physical traits are called synapomorphies. However, some specific parts of the group are well-defined. Stramenopiles are characterized by an anterior flagellum with tripartite bristles. These bristles are called mastigonemes. Alveolates are united by the presence of cortical alveoli. These are small sacs located under the cell's outer layer.

Recent studies of telonemids offer more clues about the group's history. Telonemids might be the sister group to SAR. If this is true, they would form an even larger clade called TSAR. Some researchers use the name Harosa for this group. Telonemids have tripartite hairs and peripheral vacuoles. Scientists believe these might be homologous to structures in stramenopiles and alveolates. This means the structures may have been shared by a common ancestor. It is possible that cortical alveoli actually evolved from these ancestral peripheral vacuoles.

Understanding the SAR supergroup helps us map the entire tree of life. A 2021 analysis placed Alveolata and Stramenopiles together in a group called Halvaria. In this model, Halvaria is the sister group to Rhizaria. This helps scientists organize the massive amount of life on our planet. By studying these lineages, we learn how complex cells and different ways of living first appeared. The SAR group remains a robust and essential part of modern biology.