Systematics, Taxonomy, and Evolution of <em>Urtica</em> L. (Urticaceae)

Abstract

The systematics of <i>Urtica</i> have puzzled scientists for the past 200 years and no single comprehensive attempt at understanding infrageneric relationships has been published in the past, nor have species delimitations been unequivocally established. The major aims of this study are to clarify some taxonomic problems in morphologically difficult taxa with a special emphasis placed on the European, Australian/New Zealand and Asian species. In addition, the overall phylogeny of <i>Urtica</i> based on a comprehensive sampling of the species and subspecific entities in the genus was addressed and based on this, a re-examination of the gender distribution as an important and probably unique morphological feature within angiosperms.<br /> Chapter 2 identifies a total of five morphotypes of the widespread and often weedy <i>U. dioica</i> subsp. <i>dioica</i> which are stable in cultivation and usually occur in several different regions of Europe and/or are characterized by some type of habitat preference. Infraspecific relationships of this clade have been further analysed by highly resolving next-generation-sequencing-data in chapter 8. The third chapter addresses a redefinition of <i>U. incisa</i> and allies in New Zealand and Australia, including the segregation of two new species <i>U. sykesii</i> and <i>U. perconfusa</i>. In addition, evidence for the presence of true introduced <i>U. dioica</i> subsp. <i>dioica</i> in New Zealand was found. <i>Urtica</i> from Asia is also plagued with problems in taxon differentiation. Based on a critical re-examination of morphological characters combined with molecular data, a total of four subspecies of the eastern Asian species <i>U. thunbergiana</i> is proposed (Chapter 4) and a total of five species and two subspecies are recognised within the East-Southeast Asian <i>Urtica fissa</i>-clade (Chapter 5).<br /> Chapter 6 provides the first comprehensive phylogeny of the genus <i>Urtica</i> including 61 of the 63 species recognized. The phylogenetic analyses retrieve numerous well-supported clades and suggest that the morphological characters used to distinguish and group species in the genus do not reflect phylogenetic relatedness. Eastern Asian <i>Zhengyia shennongensis</i> is sister to<i> Urtica</i> and western Eurasian <i>U. pilulifera</i> and <i>U. neubaueri</i> are sister to all other species of the genus.<br /> The evolution of <i>Urtica</i> sexual systems has so far been treated very generically in the literature; this study reveals two entirely different dimensions to this phenomenon – the distribution of different sexes between plants versus the complex geometry of their distribution on individual plants (Chapter 7). Numerous theories have been proposed for the former phenomenon, but the geometry of gender distribution on individual plants has escaped the attention of scientists. We here provide a descriptive and evolutionary framework for gender distributionin <i>Urtica</i>. We found polygamy, two types of gynodioecy and five architectural types of monoecy.