A phylogenetic tree of the expansin superfamily, including protein sequences from Arabidopsis thaliana (At), Oryza sativa (Os), Pinus species (pine) and Physcomitrella patens (moss). These sequences were selected to showcase expansin diversity. They were aligned with CLUSTALW (see Additional data file 1) and a neighbor-joining tree was constructed with MEGA 3. Bootstrap values above 60 are indicated next to the relevant node, and the four families are labeled at their roots. Clades, defined as all the descendants of the same ancestral gene in the last common ancestor of monocots and eudicots, are indicated by black bars to the right and given Roman numbers as in . This tree does not correctly resolve clades EXPA-I and EXPA-II, possibly because of changes in amino-acid usage between Arabidopsis and rice expansins . The numbers for pine sequences are from TIGR Pinus Gene Index ; GenBank accession numbers are shown for moss sequences. EXPA, α-expansin; EXPB, β-expansin; EXLA, expansin-like A; EXLB, expansin-like B.