Using Curie-point Pyrolysis Gas Chromatography Mass Spectrometry (Py-GCMS) and Direct Temperature-resolved Mass Spectrometry (DT-MS), lignin was detected in highly purified preparations (Milled Wood Lignin = MWL) of various tissues of the seagrasses Zostera marina and Posidonia oceanica. The results indicate that P. oceanica contains more lignin than Z. marina and that roots and rhizomes generally contain more lignin than leaves. It is concluded that the ability to produce lignin is not lost by the angiosperm ancestors of extant seagrasses upon their colonization of the marine environment. Relative lignin abundances in the different tissues appear to be positively correlated with life span. It is suggested that lignification contributes to the longevity of a tissue by protecting it against microbial attack, but that deposition of lignin in seagrasses is restricted to tissues that show limited growth.