A major aim in the field of evolutionary developmental biology (evo-devo) is to identify the mechanisms by which developmental novelties arise. The observation that incited the present study was the identification of a common theme across the differentiation of multiple specialised cell types in the seed plant epidermis. Tripartite transcriptional complexes composed of a MYB transcription factor, a bHLH transcription factor and a WD repeat scaffold (MYB-bHLH-WDR or MBW complexes) regulate patterns of flavonoid pigments, trichomes and root hairs in this cell layer. We reasoned that investigating the origins and diversification of the MBW complexes may give insights into the origins of these cell types. Phylogenetic analysis and interrogation of the conservation of implicated sequence motifs led us to hypothesise that the MBW complexes identified in seed plants have a single origin in an ancestral land plant. This was associated with parallel duplication events in the bHLH and MYB families and recruitment of a more deeply conserved WDR. To test our hypothesis, we undertook functional analysis of orthologues from the bryophyte Marchantia polymorpha. We found that protein-protein interactions were conserved. Further, we found that putative MBW complex members in M. polymorpha phenocopied each other with respect to flavonoid pigmentation and specialised oil body metabolism. In conclusion, we infer that the functionally disparate MBW complexes of seed plants derive from a single MBW complex ancestral to land plants. Overlap between regulated processes in bryophytes and seed plants implies that the regulation of flavonoid biosynthesis, by targeting of early flavonoid pathway genes such as Chalcone Synthase, could have been the ancestral function. We find evidence that duplication of the MYB member has repeatedly been associated with neofunctionalization of the complex in rosids, for trichome and root hair patterning, and in liverworts, for specialised metabolism in a lineage-specific organelle, the oil body.