An integrated study of ramie (Boehmeria nivea), and its wild, cultivated and feral form

Feralization, the re-establishment of wild populations from domesticated ancestors, can involve multiple parallel character reversions, and potentially also rampant gene flow with cultivated and/or naturally wild material. It hence poses great challenges for infraspecific classification, which may impede crop development, but studies on these issues are rare. Ramie (Boehmeria nivea; Urticaceae) is an important fiber crop worldwide. It has been traditionally divided into 2-4 varieties, but these are controversial. Here, 78 wild and feral individuals were sampled from 12 Chinese provinces, plus 11 cultivated individuals from farmland. We employed an integrative taxonomy approach combining multiple lines of evidence from morphology, phylogenomics, and ecology to investigate the intraspecific subdivision of B. nivea. A chi-square test of qualitative morphological characters significantly distinguished three varieties within B. nivea: var. nivea, var. tenacissima, and the recently described var. strigosa, comprising mainly cultivated, mainly feralized, and only naturally wild material respectively. The PCoA and random forest analyses indicated differences between var. strigosa and the other two varieties. However, quantitative characters could not distinguish the three varieties. None of the three varieties was monophyletic based on the phylogeny of plastome data, whereas var. strigosa was weakly supported as monophyletic based on nuclear ribosomal DNA (18S-ITS1-5.8S-ITS2-26S). Ecological niche modelling showed overlap between the potential distribution areas of var. nivea and var. tenacissima, but neither overlapped with var. strigosa. These analyses collectively demonstrate the distinctiveness of var. strigosa, but mostly did not fully separate var. nivea from var. tenacissima. Hence var. strigosa is a biologically meaningful variety, but var. tenacissima should, be synonymised within var. nivea. These results should aid the breeding and improvement of new varieties of ramie and highlight the value of integrative taxonomic methods in examining infraspecific subdivisions within species that include cultivated and feralized material.