At least 23 genera instead of one

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Abstract

Background: Iris L. s.l. is one of the most diverse and well-known genera in the Asparagales, with approximately 250–300 circumscribed species and significant economic impact. The taxonomy of the genus has suffered dramatic changes in the last century, particularly in the last decades after the application of molecular techniques. As a result several contrasting systematic arrangements are currently available to taxonomists. Many genera that were split from Iris s.str. in the past, on the basis of morphology (e.g., Hermodactylus, Iridodictyum, Juno, Pardanthopsis, and Xiphion, among others), are now a priori re-included in a very widely circumscribed Iris s.l. (incl. Belamcanda). This resulted in a more heterogeneous genus that is more difficult to define on morphological grounds. Testing congruence between taxonomic treatments and the results of recent molecular studies of Iris has never been performed, mostly due to the lack of proper taxonomic context.

Results: We generated several conventional phylogenies for Iris & outgroups using extensive sampling of taxa (187) and characters (10 plastid loci). We demonstrate that the natural history of Iris, written either as conventional molecular phylogenies or, if viewing in the context of the comparative approach, as a nested most parsimonious hierarchy of patterns, appear to be fully congruent with the narrow taxonomical treatment of the genus, restricted to the rhizomatous ‘‘bearded’’ taxa. The resulting topologies place Belamcanda, Pardanthopsis, and Gattenhofia as sisters to Iris s.str. and genus Siphonostylis as sister to Iris s.l.

Conclusion: The present study clearly justifies the splitting of Iris s.l. into at least 23 genera, 18 of which have already been accepted in the past by numerous authorities. These genera are characterized by unique combinations of partly overlapping morphological characters and biogeography. Moreover, nearly the same entities, which we here recognize at a generic rank, were for centuries frequently referred to by horticulturists as ‘‘working-name’’ groups.

Citation : Mavrodiev EV, Martı´nez-Azorı´n M, Dranishnikov P, Crespo MB (2014) At Least 23 Genera Instead of One: The Case of Iris L. s.l. (Iridaceae). PLoS ONE 9(8): e106459. doi:10.1371/journal.pone.0106459

Editor: Zhong-Jian Liu, The National Orchid Conservation Center of China; The Orchid Conservation & Research Center of Shenzhen, China

Received February 14, 2014; Accepted July 31, 2014; Published August 29, 2014 Copyright:  2014 Mavrodiev et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The authors have no support or funding to report.

Competing Interests: The authors have declared that no competing interests exist.

Email: evgeny@ufl.edu

Introduction

With approximately 250–300 species in circumscribtion, Iris s.l. is one of the most diverse and well-known genera in the Asparagales. The genus also includes a few outstanding model systems in evolutionary biology, particularly those used for studying hybridization and speciation in plants (e.g., [1,2]). Due to its popularity in the horticultural trade, Iris has significant economic impact. However the taxonomy of Iris s.l. remains complicated. Based on morphology, many genera were split from Iris s.str. and were widely accepted in the past (e.g. Hermodactylus, Iridodictyum, Juno, or Xiphion, among others. They are now a priori re-included in a widely circumscribed Iris s.l., which renders it more heterogeneous and difficult to define on morphological grounds.

The test for congruence of Iris’s taxonomy, with the results of recent molecular studies of Iris, seems to be critical, but it has never been performed in a proper way, mostly due to the lack of correct taxonomic context. Here, we present the phylogenies for the Iris s.l. & outgroups by using extensive sampling of taxa (187) and characters (10 plastid loci), establishing the largest molecular matrix yet assembled for the group.

We also paired conventional phylogenetic analyses with the three-taxon analysis (3TA) [3,4,5] of binary representations of DNA matrices of the Iris s.l. & outgroups.

We compare the obtained conventional molecular phylogenies of Iris and the most parsimonious hierarchy of patterns yielded by the three-taxon analyses, with the different taxonomical treatments of the genus, and propose a new taxonomic arrangement of Iris s.l.

Results

Figure 1 provides the detailed summary of the results. The names of the clades are given in italics due to the strong congruence with various taxonomic entities. The phylogenetic analyses of either the complete or modified supermatrix and the three-taxon statements (3TSs) binary matrices yielded similar topologies with all of the traditional infrageneric taxa of Iris s.l., resolved as well or strongly supported monophyletic groups or lineages (Figures 1–2, Figures S1–S6).

Positions of monophyletic Cryptobasis Nevski (I. subsect. Tenuifoliae Diels), I. sect. Psammiris (Spach) J.J.Taylor (I. subgen. Psammiris Spach), I. sect. Pseudoregelia Dykes (I. subgen. Pseudoevansia Baker), Lophiris nom. provis. (Iris subg. Lophiris (Tausch) C.A. Wilson), I. subgen. Crossiris Spach (I. watti Baker ex Hook.f. + I. japonica Thunb.), Juno sect. Acanthospora Rodion., J. sect. Wendelboa Rodion., Rodionenkoa nom. provis. (I. sect. Monospatha Rodion.), Spathula (Tausch) Fourr. (I. foetidissima L., I. subg. Spathula (Tausch) Spach), and Zhaoanthus nom. provis. (I. subsect. Chinensis Diels, Limniris sect. Chinensis (Diels) Rodion.) depend on the chosen method of the analysis (Figures 1–2, Figures S1–S6). Clade {Pardanthus (Belamcanda Adans. (B. chinensis (L.) Redoute´, I. domestica (L.) Goldblatt & Mabb.) + Pardanthopsis (Hance) L.W. Lenz (Pardanthopsis dichotoma (Pall.) L.W. Lenz, Iris dichotoma Pall., Pardanthus dichotomus (Pall.) Ledeb.)} and Gattenhofia Medik. (I. subsect. Vernae Diels) are sister groups of the well or strongly supported Iris s.str. (Figures 1–2, Figure S1). Siphonostylis Wern. Schulze (I. subg. Siphonostylis (Wern. Schulze) C.A. Wilson (I. ser. Unguiculares (Diels) G.H.M. Lawr. =Limniris sect. Unguiculares (Diels) Rodion.)), was confirmed as the sister group to the rest of Iris s.l. (Figure 1, Figures S1–S2). Evansia Salisb. (incl. Junopsis Wern.Schulze (I. subg. Nepalensis (Dykes) G.H.M. Lawr.)) is sister to Juno Tratt. (I. subgen. Scorpiris Spach), and {Juno + Evansia} + {Iris s.str. + Gattenhofia + Belamcanda + Pardanthopsis} are strongly supported sister clades. The monotypic genus Sclerosiphon Nevski (Iris songarica Schrenk) is a strongly supported sister to Eremiris (Spach) Rodion. (I. subgen. Eremiris Spach) and both latter groups form a a strongly supported sister clade to Joniris (Spach) Klatt (I. subg. Ioniris Spach). Clade {Sclerosiphon + Eremiris + Joniris} is a strongly supported sister of Limniris (Tausch) Rchb. s.l. Iridodictyum Rodion (Iris subgen. Hermodactyloides Spach; I. sect. Reticulata Dykes) (incl. Iris sect. Brevituba B. Mathew (I. pamphylica Hedge)), (Cryptobasis Nevski (conventional phylogenies only) + Hermodactylus Mill. (I. subgen. Hermodactylus (Tourn.) Sweet (I. tuberosa L.)), Syrianthus nom. provis. (I. masia Dykes, I. subg. Limniris (Tausch) Spach subsect. Syriacae Diels), Xiphion Mill. (I. sect. Xiphion (Mill.) Tausch), Alatavia kolpakowskiana (Regel) Rodion. (Iridodictyum sect. Monolepis Rodion., Iris kolpakowskiana Regel), and Chamaeiris Medik. (Xyridion (Tausch) Fourr., I. subgen. Xyridion Spach (incl. Spathula)) formed a grade with the partly conflict levels of support (Figure 1–2, Figures S1– S6).

Juno sect. Physocaulon Rodion. is a strongly supported sister clade to the rest of the Juno, I. sect. Brevituba (I. pamphylica) is strongly supported sister to Iridodictyum, and Chamaeiris sogdiana (Bunge) M.B.Crespo (Iris sogdiana Bunge, Xyridion sogdianum (Bunge) Nevski) is a sister to the rest of the Chamaeiris (Figure 1–2, Figures S1–S6).

Several species sampled in more than one infraspecific taxa, appeared to be non-monophyletic (I. caucasica Hoffm., I. hartwegii Baker, I. potaninii Maxim. and others) (Figure 2).