**Abstract**

Glycosylation substantially contributes to the physicochemical properties of proteins, and hence also cell walls. Moreover, they are key factors for the recognition of free or cell-bound glycoproteins by internal and external interaction partners. Green plants get by with a highly conserved, limited number of modifications of the pan-eukaryotic basic N-glycan structure. In detail, these are fucosylation of the innermost N-acetylglucosamine residue in 3-position, which renders plant glycoproteins immunogenic to mammals; xylosylation of the branching mannose; frequent occurrence of small N-glycans terminating with mannose or decoration of the antennae with Lewis A determinants. Bryophytes share all these features, but some mosses additionally display two peculiarities not seen in vascular plants. Many mosses exhibit 2,6-di-O-methylated mannose on the 6-arm and some mosses contain modified Lewis A termini with an as yet unspecified methyl pentose. Neither the responsible enzymes nor the function of these novel glycan features is currently known. Targeted glycoengineering of the moss *Physcomitrella patens* (Hedw.) Bruch & Schimp can allow the production of biopharmaceutical glycoproteins that are difficult to express in more established systems.

**Keywords:** glycoprotein, N-glycan, methyl-mannose, methylation, biopharmaceuticals
