1 CITES. http://www.cites.org/eng/app/appendices.php. Appendices I, II and III. (2015).
2 Zeng, S. et al. In vitro propagation of Paphiopedilum orchids. Critical Reviews in Biotechnology 36, 521-534 (2016).
3 Zhang, Y. et al. Embryo development in association with asymbiotic seed germination in vitro of Paphiopedilum armeniacum SC Chen et FY Liu. Scientific Reports 5, 16356 (2015).
4 Steinbrecher, T. & Leubner-Metzger, G. The biomechanics of seed germination. Journal of Experimental Botany 68, 765-783, doi:10.1093/jxb/erw428 (2017).
5 Tang, Y., Zhao, D., Meng, J. & Tao, J. EGTA reduces the inflorescence stem mechanical strength of herbaceous peony by modifying secondary wall biosynthesis. Horticulture Research 6, 36 (2019).
6 Pierce, S., Spada, A., Caporali, E., Ceriani, R. M. & Buffa, G. Enzymatic scarification of Anacamptis morio (Orchidaceae) seed facilitates lignin degradation, water uptake and germination. Plant Biology (2018).
7 Yeung, E. C. A perspective on orchid seed and protocorm development. Botanical Studies 58, 33 (2017).
8 Pierce, S. & Cerabolini, B. Asymbiotic germination of the White Mountain Orchid (Pseudorchis albida) from immature seed on media enriched with complex organics or phytohormones. Seed Science Technology 39, 199-203 (2011).
9 Barsberg, S., Rasmussen, H. N. & Kodahl, N. Composition of Cypripedium calceolus (Orchidaceae) seeds analyzed by attenuated total reflectance IR spectroscopy: in search of understanding longevity in the ground. American journal of botany 100, 2066-2073 (2013).
10 Vanholme, R., Demedts, B., Morreel, K., Ralph, J. & Boerjan, W. Lignin biosynthesis and structure. Plant physiology 153, 895-905 (2010).
11 Chen, F. et al. Novel seed coat lignins in the Cactaceae: structure, distribution and implications for the evolution of lignin diversity. The Plant Journal 73, 201-211 (2013).
12 Barsberg, S. T., Lee, Y.-I. & Rasmussen, H. N. Development of C-lignin with G/S-lignin and lipids in orchid seed coats–an unexpected diversity exposed by ATR-FT-IR spectroscopy. Seed Science Research 28, 41-51 (2018).
13 Chen, F., Tobimatsu, Y., Havkin-Frenkel, D., Dixon, R. A. & Ralph, J. A polymer of caffeyl alcohol in plant seeds. Proceedings of the National Academy of Sciences 109, 1772-1777, doi:10.1073/pnas.1120992109 (2012).
14 Xie, M. et al. Regulation of lignin biosynthesis and its role in growth-defense tradeoffs. Frontiers in plant science 9, 1427 (2018).
15 Hao, Z. & Mohnen, D. A review of xylan and lignin biosynthesis: foundation for studying Arabidopsis irregular xylem mutants with pleiotropic phenotypes. Critical Reviews in Biochemistry Molecular Biology 49, 212-241 (2014).
16 Stone, M. L. et al. Reductive Catalytic Fractionation of C-Lignin. ACS Sustainable Chemistry 6, 11211-11218 (2018).
17 Tobimatsu, Y. et al. Coexistence but independent biosynthesis of catechyl and guaiacyl/syringyl lignin polymers in seed coats. The Plant Cell 25, 2587-2600 (2013).
18 Wagner, A. et al. CCoAOMT suppression modifies lignin composition in Pinus radiata. The Plant Journal 67, 119-129 (2011).
19 Barthlott, W., Große-Veldmann, B., Korotkova, N. J. A. s. e. m. s. T. N. y. R. M., editores. Berlin: Botanic Garden & Berlin-Englera, B. M. Orchid seed diversity. (2014).
20 Kinderen, G. Abscisic acid in terrestrial orchid seeds: a possible impact on their germination. Lindleyana 2 (1987).
21 Nambara, E. et al. Abscisic acid and the control of seed dormancy and germination. Seed Sci Res 20, doi:10.1017/S0960258510000012 (2010).
22 Lee, Y. I., Chung, M. C., Yeung, E. C. & Lee, N. Dynamic distribution and the role of abscisic acid during seed development of a lady’s slipper orchid, Cypripedium formosanum. Ann Bot 116, doi:10.1093/aob/mcv079 (2015).
23 Özparpucu, M. et al. Unravelling the impact of lignin on cell wall mechanics: a comprehensive study on young poplar trees downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD). The Plant Journal 91, 480-490 (2017).
24 Zhang, L. et al. Origin and mechanism of crassulacean acid metabolism in orchids as implied by comparative transcriptomics and genomics of the carbon fixation pathway. The Plant Journal 86, 175-185 (2016).
25 Zhang, G.-Q. et al. The Dendrobium catenatum Lindl. genome sequence provides insights into polysaccharide synthase, floral development and adaptive evolution. Scientific reports 6, 19029 (2016).
26 Zhong, R., Morrison, W. H., Himmelsbach, D. S., Poole, F. L. & Ye, Z.-H. Essential role of caffeoyl coenzyme A O-methyltransferase in lignin biosynthesis in woody poplar plants. Plant Physiology 124, 563-578 (2000).
27 Marita, J. M. et al. Structural and compositional modifications in lignin of transgenic alfalfa down-regulated in caffeic acid 3-O-methyltransferase and caffeoyl coenzyme A 3-O-methyltransferase. Phytochemistry 62, 53-65 (2003).
28 Do, C.-T. et al. Both caffeoyl Coenzyme A 3-O-methyltransferase 1 and caffeic acid O-methyltransferase 1 are involved in redundant functions for lignin, flavonoids and sinapoyl malate biosynthesis in Arabidopsis. Planta 226, 1117-1129 (2007).
29 Zhuo, C. et al. Enzymatic basis for C‐lignin monomer biosynthesis in the seed coat of Cleome hassleriana. The Plant Journal 99, 506-520 (2019).
30 Zhao, Q. & Dixon, R. A. Transcriptional networks for lignin biosynthesis: more complex than we thought? Trends in plant science 16, 227-233 (2011).
31 Karpinska, B. et al. MYB transcription factors are differentially expressed and regulated during secondary vascular tissue development in hybrid aspen. 56, 255-270 (2004).
32 Jin, H. et al. Transcriptional repression by AtMYB4 controls production of UV‐protecting sunscreens in Arabidopsis. 19, 6150-6161 (2000).
33 Patzlaff, A. et al. Characterisation of a pine MYB that regulates lignification. The Plant Journal 36, 743-754 (2003).
34 Zeng, S. et al. Asymbiotic seed germination, seedling development and reintroduction of Paphiopedilum wardii Sumerh., an endangered terrestrial orchid. Scientia Horticulturae 138, 198-209 (2012).
35 Pan, X., Welti, R. & Wang, X. Quantitative analysis of major plant hormones in crude plant extracts by high-performance liquid chromatography–mass spectrometry. Nature protocols 5, 986 (2010).
36 Fang, L. et al. Loss of inositol phosphorylceramide sphingolipid mannosylation induces plant immune responses and reduces cellulose content in Arabidopsis. The Plant Cell 28, 2991-3004 (2016).
37 Del Río, J. C. et al. Structural characterization of wheat straw lignin as revealed by analytical pyrolysis, 2D-NMR, and reductive cleavage methods. Journal of agricultural food chemistry 60, 5922-5935 (2012).
38 Del Río, J. C. & Gutiérrez, A. Chemical composition of abaca (Musa textilis) leaf fibers used for manufacturing of high quality paper pulps. Journal of agricultural food chemistry 54, 4600-4610 (2006).
39 Ralph, J. & Hatfield, R. D. Pyrolysis-GC-MS characterization of forage materials. Journal of Agricultural Food Chemistry 39, 1426-1437 (1991).
40 Kim, H. & Ralph, J. Solution-state 2D NMR of ball-milled plant cell wall gels in DMSO-d6/pyridine-d5. Organic biomolecular chemistry 8, 576-591 (2010).
41 Haas, B. J. et al. De novo transcript sequence reconstruction from RNA-seq using the Trinity platform for reference generation and analysis. Nature Protocols 8, 1494 (2013).
42 Deng, Y. et al. Integrated nr database in protein annotation system and its localization. Comput Eng 32, 71-74 (2006).
43 Apweiler, R. et al. UniProt: the universal protein knowledgebase. Nucleic acids research 32, D115-D119 (2004).
44 Tatusov, R. L., Galperin, M. Y., Natale, D. A. & Koonin, E. V. The COG database: a tool for genome-scale analysis of protein functions and evolution. Nucleic acids research 28, 33-36 (2000).
45 Consortium, G. O. The Gene Ontology (GO) database and informatics resource. Nucleic acids research 32, D258-D261 (2004).