Unsung and understudied: plastids involved in secondary growth

•Plastids are key for production of aromatic amino acids—monolignol precursors.•We currently know very little about plastid biology during secondary growth.•Evidence exists for structural and metabolic specialization of plastids in xylem.•A new nomenclature for a distinct organelle—the ‘xyloplast’, is motivated.•Exploring this biology further is integral to modelling xylogenesis as a system.