A new classification of C4- Atriplex species in Russia, with the first alien record of Atriplexflabellum (Chenopodiaceae, Amaranthaceae) from North Siberia

For a long time, the systematics of Atriplex was based solely on morphological characters and leaf anatomy. The latest worldwide phylogenetic study of Atriplex significantly improved our knowledge about the relationships within the genus, but a new classification has not been put forward thus far. Here we re-evaluate the taxonomy of C(4)-species of Atriplex that are native to Russia. Seven species are classified into two sections, A.sect.Obione (incl. A.sect.Sclerocalymma, syn. nov.) (A.altaica, A.centralasiatica, A.rosea, A.sibirica, and A.sphaeromorpha), and A.sect.Obionopsis (incl. A.sect.Psammophila, syn. nov.) (A.fominii and A.tatarica). Although the majority of Eurasian C(4)-species have similar morphology, leafy inflorescence is a typical character for A.sect.Obione. The members of A.sect.Obionopsis are characterised mostly by aphyllous inflorescences, but some species (A.laciniata, A.pratovii, and A.tornabenei) have leafy inflorescences. Geographically, almost all members of A.sect.Obione are confined to Central Asia, although A.rosea is a typical Mediterranean element and A.argentea occurs in North America. The representatives of A.sect.Obionopsis are distributed mostly in the Mediterranean and the Irano-Turanian floristic region. The alien status of A.rosea, A.sibirica and A.tatarica is discussed. Atriplexflabellum, a desert species from the Irano-Turanian region, is reported for the first time from Russia (Yamalo-Nenets Autonomous District, North Siberia) as a casual alien. This species occupies a phylogenetic position distant from both aforementioned sections. An identification key to all C(4)-species of the genus growing in Russia is given, and a sectional checklist with updated nomenclature and revised synonymy is provided.