Astragalus zibaishanensis sp. nov. (Fabaceae), a new species from Shaanxi, China

<i>Astragalus zibaishanensis</i> <b>sp. nov.</b> (Fabaceae) is described and illustrated from Shaanxi, China. This new species is similar to <i>Astragalus monadelphus</i>, <i>A. xitaibaicus</i> and <i>A. neomonodelphus</i> by having yellow petals, pseudomonadelphous androecium, and stipitate legumes, but can be distinguished by its stem 0.9-1.5 mm in diameter; leaflets 5-7, hairy adaxially and abaxially; calyx teeth triangular, ca. 0.5 mm long; standard 17-20 mm long; wings 18-21 mm long; keels 17-20 mm long; pistil glabrous; legume glabrous, with a stipe 10-11 mm long. <i>Astragalus zibaishanensis</i> is unique in <i>Astragalus</i> by having pseudomonadelphous androecium. Phylogenetic analyses confirm that the new species is a member of A. sect. Cenantrum. The nuclear ITS tree shows that <i>A. zibaishanensis</i> forms a clade with <i>A. henryi</i>, <i>A. umbellatus</i>, <i>A. chilienshanensis</i>, <i>A. moellendorffii</i>, <i>A. przewalskii</i>, <i>A. monadelphus</i>, <i>A. xitaibaicus</i> and <i>A. neomonodelphus</i>.