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.
Highlights
The genus Atraphaxis L. (Linnaeus, 1753) (Polygonaceae) includes ca. 30 species distributed from South-East Europe and North-East Africa to East Siberia, China, and Mongolia with its centers of taxonomic diversity in South-West and Central Asia (Bentham & Hooker, 1880; Pavlov, 1936; Webb, 1964; Cullen, 1967; Rechinger & SchimanCzeika, 1968; Lovelius, 1978; Lovelius, 1979; Borodina, 1989; Brandbyge, 1993; Cherepanov, 1995; Gubanov, 1996; Bao & Grabovskaya-Borodina, 2003; Baikov, 2012)
Strong similarity in petiole and stem anatomy supports the placement of Atraphaxis into the tribe Polygoneae Meisn. emend Haraldson along with Polygonum L., Polygonella Michx., Oxygonum Burch., Pteropyrum Jaub. et Spach, Calligonum L., and Fagopyrum Mill. (Haraldson, 1978), that greatly corresponds to the results of recent molecular studies, the latest of which revealed the composition of the tribe Polygoneae, subfamily Polygonoideae (Galasso et al, 2009; Schuster, Wilson & Kron, 2011a; Schuster, Reveal & Kron, 2011b)
ITS phylogeny The results of Maximum Likelihood (ML) and BI of the ITS matrix of Polygoneae (Fig. 1), with Knorringia taken as an outgroup, show that the members of the tribe form a highly supported clade (0.99/1.0)
Summary
The genus Atraphaxis L. (Linnaeus, 1753) (Polygonaceae) includes ca. 30 species distributed from South-East Europe and North-East Africa to East Siberia, China, and Mongolia with its centers of taxonomic diversity in South-West and Central Asia (Bentham & Hooker, 1880; Pavlov, 1936; Webb, 1964; Cullen, 1967; Rechinger & SchimanCzeika, 1968; Lovelius, 1978; Lovelius, 1979; Borodina, 1989; Brandbyge, 1993; Cherepanov, 1995; Gubanov, 1996; Bao & Grabovskaya-Borodina, 2003; Baikov, 2012). According to the phylogenetic analyses of Galasso et al (2009), based on cpDNA sequence data (rbcL cpDNA region), the tribe Polygoneae comprises Polygonum 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 performed. S. Tavakkoli) was confirmed to be a sister of the clade The generic composition of the tribe Polygoneae requires future reappraisals
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