Phylogeny and infrageneric classification of tulips

Abstract

Despite many studies conducted over a period of nearly two centuries since Reboul, who was the first to classify tulips as subgeneric level, there is still no consensus among researchers regarding the infrageneric classification of tulips. Nevertheless, in recent years, efforts to solve this taxonomic problem have been increasing. However, phylogenetic studies covering all species of a genus or at least with species representatives of all subgeneric taxonomy worldwide are very scarce. The main difference of the current study from previous studies is that it is a larger study focused on solving this problem by considering all perspectives together, covering many geographical areas and species in global distribution. For this purpose, we examined the phylogenetic relationships of the genus Tulipa with 82 accessions from 45 Tulipa species and six accessions from two Amana and three Erythronium species, and we positioned our results by discussing them in light of previous morphological, geographical, molecular and anatomical data. We investigated the phylogenetic relationships in the genus using DNA sequences from the internal transcribed spacer region of nuclear ribosomal DNA. The 45 species of Tulipa formed a monophyletic clade. Genera Amana and Erythronium were clustered as outgroups. In the genus Tulipa, two major clades were obtained; the first clade belonged to subgenus Orithyia. The second clade separated subgenus Tulipa and subgenera Eriostemones+Clusianae. Then, Eriostemones and Clusianae subgenera formed two separate clusters. Subgenus Eriostemones separated two main clusters; section Biflores and section Sylvestres. On the other hand, all previously proposed sections and series under the subgenus Tulipa were grouped into a single clade. This situation agrees with previous biosystematic data highlighting the morphological overlap of most of the sections and with previous molecular data showing that many sections are not monophyletic. Consequently, we propose a taxonomic concept consisting of four subgenera and two sections.