Pelagibacterales

Currently, the order is divided into five subgroups: • Subgroup Ia, open ocean, crown group — includes P. ubique HTCC1062 • Subgroup Ib, open ocean, sister clade to Ia • Subgroup II, coastal, basal to Ia + Ib • Subgroup III, brackish, basal to I + II along with its sister clade IV • Subgroup IV, also known as the LD12 clade, freshwater • Subgroup V, which includes alphaproteobacterium HIMB59, basal to the remainder The above results in a cladogram of the Pelagibacterales as follows: ==Phylogenetic placement and endosymbiotic theory==

A 2011 study by researchers of the University of Hawaiʻi at Mānoa and Oregon State University, indicated that SAR11 could be the ancestor of mitochondria in most eukaryotic cells. ==See also==