Final answer:
The SAR clade is a classification for stramenopiles, alveolates, and rhizarians, united by recent molecular analysis of their genetic material. This reflects a significant shift from traditional classifications to a phylogenetic approach based on ribosomal RNA data, as advanced by Carl Woese.
Step-by-step explanation:
The SAR clade is a classification that uses the first letters of the three groups of organisms within it, the stramenopiles, the alveolates, and the rhizarians. This classification exists because of recent molecular analysis that suggests these groups are closely related to one another. Traditionally, organisms were classified into five kingdoms based on morphological characteristics, but this was significantly revised after the pioneering work of Carl Woese and his colleagues. They proposed a new classification system based on genetic information from ribosomal RNA (SSU rRNA), which led to the identification of three domains of life.
These phylogenetic studies provided deeper insights into evolutionary relationships, grouping organisms in a way that reflects common ancestry and genetic lineage rather than mere physical resemblance. The use of molecular techniques, such as comparisons of SSU rRNA sequences, has led to the recognition of more accurate evolutionary relationships between organisms and has given rise to newly understood supergroups like the SAR clade.