Plant cell walls are a complex network of polysaccharides that affect metabolic function, structurally support, and protect the cell. Inherent recalcitrance and complexity of cell walls is a challenging limitation to engineering their structures in most land plants. The common liverwort, Marchantia polymorpha , is an early non-vascular land plant and a promising model system for synthetic biology. Marchantia has a haploid dominant life cycle, low genetic redundancy, and rapid growth. We have implemented protocols to stably transform Marchantia plant tissues using Agrobacterium tumefaciens as a vector to insert transgenes of interest and/or edit the genome with CRISPR/Cas9. For example, the Arabidopsis thaliana genome contains nine Cellulose Synthase-Like A (CSLA) genes encoding putative (gluco)mannan synthases, but Marchantia only encodes one CSLA homolog, greatly simplifying its functional characterization. Biochemical analysis of cell wall polysaccharides has shown notable differences between Marchantia , Arabidopsis , and other land plants. Knocking down and/or eliminating the MpCSLA gene, which acts as a bona fide mannan synthase in yeast, will reveal the biological functions of CSLA in vivo and its effects on other cell wall components. Marchantia therefore offers a powerful plant system to decipher the genetic parts that underpin cell wall traits or to introduce new-to-nature carbohydrate properties.