Bikonta

Bikonta (bikonts) is a historic eukaryotic clade proposed by Thomas Cavalier-Smith to contrast with unikonts. The name derives from Greek bi- meaning two and kontos meaning pole or flagellum, reflecting the hypothesis that the deepest ancestral eukaryote possessed two flagellar roots, in contrast to unikonts, which have a single flagellum. The concept was intended to group lineages based on this early cellular feature and related morphological traits.

Traditionally included in Bikonta are major lineages such as the Archaeplastida (land plants, green and red algae, and related groups) and the SAR supergroup (Stramenopiles, Alveolates, and Rhizaria). In older classifications, other lineages such as Excavata and certain endosymbiotic groups were sometimes placed within Bikonta as well. However, the exact composition has varied across analyses, and the placement of some groups remains controversial.

In modern phylogenetics, the monophyly of Bikonta as a single clade has repeatedly been questioned, and many trees recover a mix of relationships that do not support Bikonta as a natural, umbrella lineage. Consequently, the term is used less frequently in contemporary systematics, with researchers instead referring to the constituent clades—such as Opisthokonta, Amoebozoa, Archaeplastida, and SAR—without invoking Bikonta as a unified group.

Overall, Bikonta represents a historical framework for organizing eukaryotic diversity around a two-flagellate ancestry, but its status as a coherent, monophyletic group remains uncertain.

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