Chen F., Tobimatsu Y., Jackson L., Nakashima J., Ralph J., Dixon R. A., Novel seed coat lignins in the Cactaceae: structure, distribution and implications for the evolution of lignin diversity, The Plant Journal, 2013, 73(2):201-211, doi: 10.1111/tpj.12012
Chemical characterisation of seed walls in 130 cactus species using thioacidolysis, GC-MS, NMR and microscopy. The paper documents catechyl lignin, unusual polymers of 5-hydroxyguaiacyl units in former Escobaria, typical G/S lignin and cases of undetectable lignin. Comparison with vegetative organs indicates the specificity of seed wall chemistry and leads to hypotheses of biosynthetic regulation.