A paradigm about Rhamnogalacturonans II (RGII) is their strictly conserved structure within a given plant. We developed and further employed a fast structural characterization method based on chromatography and mass spectrometry, allowing the analysis of RGII side chains from microgram amounts of cell wall. We actually found RGII structures to be much more diverse than described up to now. In chain A of wild type plants, up to 45% of the L-fucose is substituted by L-galactose, state seemingly uncorrelated with RGII dimerization capacity. This led us to a complete reinvestigation of RGII structures of the Arabidopsis thaliana fucose deficient mutant mur1, which gave insights on RGII chain A biosynthesis and suggested that chains A truncation, rather than L-fucose to L-galactose substitution, is responsible for mur1 dwarf phenotype. Mass spectrometry data of chain A coupled with NMR analysis revealed a high degree of methyl esterification of its glucuronic acid giving a plausible explanation to the yet puzzling RGII antibody recognition. The β-galacturonic acid of chain A exhibits up to two methyl etherifications in an organ specific manner. Combined with variation in side chain B length, this gives rise to a family of RGII structures instead of the unique structure described until now and paves the way to studies considering physiological roles of the modulation of RGII composition. This article is protected by copyright. All rights reserved.