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

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.