Algal evolution: A touch of brown in a Paleozoic sea of greens and reds.

Previous molecular clock studies indicated a Mesozoic origin for the brown algae (Phaeophyceae). New research based on phylogenetic evidence challenges this notion and provides novel insights into the origin and diversification of brown algae, which includes multiple transitions within the group from isogamy to oogamy (and back again!).

A multi-locus time-calibrated phylogeny of the siphonous green algae.

The siphonous green algae are an assemblage of seaweeds that consist of a single giant cell. They comprise two sister orders, the Bryopsidales and Dasycladales. We infer the phylogenetic relationships among the siphonous green algae based on a five-locus data matrix and analyze temporal aspects of their diversification using relaxed molecular clock methods calibrated with the fossil record. The multi-locus approach resolves much of the previous phylogenetic uncertainty, but the radiation of families belonging to the core Halimedineae remains unresolved. In the Bryopsidales, three main clades were inferred, two of which correspond to previously described suborders (Bryopsidineae and Halimedineae) and a third lineage that contains only the limestone-boring genus Ostreobium. Relaxed molecular clock models indicate a Neoproterozoic origin of the siphonous green algae and a Paleozoic diversification of the orders into their families. The inferred node ages are used to resolve conflicting hypotheses about species ages in the tropical marine alga Halimeda.