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Phylogenetic relationships in the tribes Schizopetaleae and Thelypodieae (Brassicaceae) based on nuclear ribosomal ITS region and plastid ndhF DNA sequences

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Abstract:

Sequence data from the nuclear ribosomal internal transcribed spacer (ITS) region and plastid gene ndhF of 95 species, represented by 147 accessions, were used to determine the tribal limits, monophyly status, and phylogenetic intra-tribal relationships of genera within the New World tribe Schizopetaleae (formerly Thelypodieae; Brassicaceae). Maximum parsimony, Bayesian, and maximum-likelihood analyses all support the separate recognition of three distinct and generally well-supported clades. The largest corresponds to the North–South American Thelypodieae (27 genera: Catadysia, Caulanthus, Chaunanthus, Chilocardamum, Chlorocrambe, Coelophragmus, Dictyophragmus, Dryopetalon, Englerocharis, Hesperidanthus, Mostacillastrum, Neuontobotrys, Polypsecadium, Pringlea, Pterygiosperma, Romanschulzia, Sibara, Sibaropsis, Stanleya, Streptanthella, Streptanthus, Thelypodiopsis, Thelypodium, Thysanocarpus, Warea, Weberbauera, and Werdermannia). The remaining six South American Schizopetaleae genera were divided into two clades: SCHIZ I of four genera (Aschersoniodoxa, Brayopsis, Eudema, and Onuris) and SCHIZ II Schizopetaleae s.str.: Mathewsia, and Schizopetalon). Resolution within the Thelypodieae clade was limited in both the ITS- and ndhF-based phylogenies. Based on ITS sequence data, elements of the Old World tribe Brassiceae were sister to the Thelypodieae, whereas the ndhF data strongly supported the Sisymbrieae as sister to the Thelypodieae, and the Brassiceae as sister to both tribes. Sister groups to the Schizopetaleae clades I and II were not clearly resolved. Morphological and cytological data support the separation of these three clades. In SCHIZ II, the sepals are always erect to form a closed tube, and the trichomes are mostly dendritic, although other types also occur. In both the Thelypodieae and SCHIZ I clades, the sepals are variously oriented but never form a closed tube, whereas the trichomes are either absent, or simple, forked, or rarely dendritic. The latter clade differs from both SCHIZ II and Thelypodieae by lacking trichomes or rarely having forked ones and by having exclusively basal, entire leaves. Thelypodieae circumscription should be restricted in future to the Thelypodieae clade, Schizopetaleae circumscription to the SCHIZ II clade, while a new tribe is needed for the SCHIZ I clade.

Les auteurs ont utilisé les données des séquences provenant de l'espaceur interne transcrit (ITS) de l'ADN nucléique ribosomal et du gène plastidique ndhF de 95 espèces représentant 147 accessions, afin de déterminer les limites tribales, le statut monophylétique et les relations phylogénétiques intra-tribales des genres, chez les Schizopetalae (anciennement Thelypodieae) (Brassicaceae). Les analyses de parcimonie, Bayésiennes et de ressemblance la plus probable supportent toutes la reconnaissance de trois clades distincts et généralement bien supportés. Le plus grand de ces clades correspond au Thelypodieae des Amériques du Nord et du Sud (27 genres: Catadysia, Caulanthus, Chaunanthus, Chilocardamum, Chlorocrambe, Coelophragmus, Dictyophragmus, Dryopetalon, Englerocharis, Hesperidanthus, Mostacillastrum, Neuontobotrys, Polypsecadium, Pringlea, Pterygiosperma, Romanschulzia, Sibara, Sibaropsis, Stanleya, Streptanthella, Streptanthus, Thelypodiopsis, Thelypodium, Thysanocarpus, Warea, Weberbauera, and Werdermannia). On divise les six genres restants des Schizopetaleae de l'Amérique du Sud en deux clades: SCHIZ I avec 4 genres (Aschersoniodoxa, Brayopsis, Eudema, and Onuris) et SCHIZ II Schizopetalae s.str. (Mathewsia, and Schizopetalon). La résolution au sein du clade Thelypodieae reste limitée à la fois chez les phylogénies basées sur les ITS et le gène ndhF. En se basant sur les données des séquences ITS, les éléments de la tribu des Brassiceae du Nouveau Monde sont apparentés aux Thelypodieae, alors que les données provenant du gène ndhF supportent les Sisymbrieae comme apparentés aux Thelypodieae et les Brassiceae comme apparentés aux deux tribus. On n'arrive pas à résoudre clairement les groupes apparentés aux clades I et II des Schizopetalae. Les données morphologiques et cytologiques supportent la séparation de ces trois clades. Chez les clades Thelypodieae et SCHIZ I, les sépales prennent différentes orientations, mais ne forment jamais un tube fermé, alors que les trichomes sont soit absents, ou encore simples, fourchus ou rarement dendritiques. Ce dernier clade diffère à la fois des clades SCHIZ II et Thelypodieae, par l'absence de trichomes ou de rares trichomes fourchus ainsi que la présence de feuilles entières exclusivement basales. La délimitation des Thelypodieae devrait à l'avenir se limiter au clade des Thelypodieae, la délimitation des Schizopetalae au clade SCHIZ II, alors qu'on doit créer une nouvelle tribu pour accommoder le clade SCHIZ I.

Document Type: Research Article

Publication date: 2009-10-01

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  • Published since 1929, this monthly journal features comprehensive research articles and notes in all segments of plant sciences, including cell and molecular biology, ecology, mycology and plant-microbe interactions, phycology, physiology and biochemistry, structure and development, genetics, systematics, and phytogeography. It also publishes commentary and review articles on topics of current interest, contributed by internationally recognized scientists.

    Previously published as the Canadian Journal of Botany
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