What is Atraphaxis L. (Polygonaceae, Polygoneae): cryptic taxa and resolved taxonomic complexity instead of the formal lumping and the lack of morphological synapomorphies

Olga V Yurtseva; Oxana I Kuznetsova; Maria E Mavrodieva; Evgeny V Mavrodiev

doi:10.7717/peerj.1977

What is Atraphaxis L. (Polygonaceae, Polygoneae): cryptic taxa and resolved taxonomic complexity instead of the formal lumping and the lack of morphological synapomorphies

PeerJ. 2016 May 3:4:e1977. doi: 10.7717/peerj.1977. eCollection 2016.

Authors

Olga V Yurtseva¹, Oxana I Kuznetsova², Maria E Mavrodieva³, Evgeny V Mavrodiev⁴

Affiliations

¹ Faculty of Biology, Department of Higher Plants, M.V. Lomonosov Moscow State University , Moscow , Russia.
² Herbarium, Tsitsin Main Botanical Garden, Russian Academy of Sciences , Moscow , Russia.
³ Eastside High School , Gainesville, Florida , USA.
⁴ Florida Museum of Natural History, University of Florida , Gainesville, Florida , USA.

Abstract

Background: The recently proposed recircumscription of the genus Atraphaxis (incl. Atraphaxis section Ovczinnikovia O.V. Yurtseva ex. S. Tavakkoli and Polygonum sect. Spinescentia Boissier (=A. sect. Polygonoides S. Tavakkoli, Kaz. Osaloo & Mozaff.) makes this genus fairly heterogeneous and therefore almost undefinable based on morphology. A critical comprehensive reappraisal of the group is necessary.

Methods: Using the DNA sequence data (ITS1&2 regions of nrDNA and combined trnL intron + trnL-F IGS and rpl32-trnL((UAG)) IGS regions of plastid genome), Maximum Likelihood (ML) and Bayesian analyses (BI) were applied for phylogenetic reconstructions of the tribe Polygoneae with special attention to Atraphaxis, and related taxa. Maximum parsimony reconstructions of the evolution of perianth morphology and sporoderm ornamentation in the tribe Polygoneae were also performed. Life history, morphology of shoots, leaf blades, ocreas, perianth and achene morphology, ultrasculpture of achene surface, and pollen morphology were compared, and SEM and LM images were provided.

Principal findings: The genera Atraphaxis and Polygonum were found to be widely polyphyletic. The rarest and morphologically remarkable endemic of Tian-Shan and Pamir Atraphaxis ovczinnikovii (Atraphaxis sect. Ovczinnikovia O.V. Yurtseva ex. S. Tavakkoli) was confirmed to be a sister of the clade (Atraphaxis + Polygonum sect. Spinescentia) in plastid topology. The genus Bactria (=Atraphaxis sect. Ovczinnikovia), which circumscribes two species, is newly established as a result of this analyses. Morphological data confirm the originality of the taxon.

Discussion: We are arguing for a narrow delimitation of Atraphaxis with petalloid segments and striato-perforate sporoderm ornamentation as morphological synapomorphies. The recently proposed inclusion of Polygonum sect. Spinescentia in Atraphaxis is fairly questionable from a morphological standpoint. The rank of Polygonum sect. Spinescentia requires further clarification. The generic composition of the tribe Polygoneae also requires future reappraisals.

Keywords: Atraphaxis; Molecular phylogeny; Perianth morphology; Polygonaceae; Polygonum; Sporoderm ornamentation; Taxonomy.

Grants and funding

The experimental part of the work (molecular experiments) was carried out with the support (to OVY and OIK) of the Russian Foundation for Basic Research (RFBR) (Project No. 11-04-01300-a), and (to OVY) of the Russian Science Foundation (RNF) (Project No. 14-50-00029). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.