Species subdivision of ramie (Boehmeria nivea; Urticaceae), a species
with wild, domesticated and feral forms, based on integrative taxonomy
Abstract
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 traits significantly
distinguished three varieties within B. nivea: var. nivea, var.
tenacissima and the recently described, var. strigosa, comprising
respectively mainly cultivated, mainly feralized, and only naturally
wild material. The morphological PCoA and random forest analyses both
indicated differences between var. strigosa and the other two varieties.
However, quantitative traits cannot distinguish the three varieties. No
variety was monophyletic according to phylogenetic analysis of plastome
data, whereas var. strigosa was weakly supported as monophyletic based
on nuclear ribosomal DNA (18S-ITS1-5.8S-ITS2-26S). Ecological niche
simulation 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 highlights the value of integrative taxonomic methods in
examining infraspecific subdivisions within species that include
cultivated and feralized material.