The phylogeny of Errazurizia (Fabaceae: Amorpheae) and description of the new monotypic genus Pictarena

<p><em>Errazurizia</em> (Fabaceae) is a genus comprised of four species of New World desert shrubs with an ambiguous evolutionary history. Prior studies determined the North American species of Errazurizia were polyphyletic and the relationship of <em>E</em>. <em>rotundata</em> with other genera in the tribe Amorpheae remained undetermined. The sole South American species, which is also the type species, has never been included in a molecular study. We inferred the phylogenetic relationships of <em>Errazurizia</em> and six closely related genera using data from the cpDNA genome and nrDNA cistron from reference-guided assemblies. Maximum likelihood and Bayesian analyses found two of the North American and the South American species were a monophyletic group, but that <em>E</em>. <em>rotundata</em> was sister to the monotypic genus <em>Parryella</em>. Gland and pollen surface characters confirm the close relationship between <em>P</em>. <em>filifolia</em> and <em>E</em>. <em>rotundata</em>. Cytonuclear discordance yielded partially incongruent tree topologies, and while the cpDNA phylogeny indicated a monophyletic Amorpha was sister to the <em>E</em>. <em>rotundata</em> and <em>P</em>. <em>filifolia</em> clade, the nrDNA cistron phylogeny recovered a paraphyletic <em>Amorpha</em>, with <em>A</em>. <em>californica</em> sister to the <em>E</em>. <em>rotundata</em> and <em>P</em>. <em>filifolia</em> clade. Molecular and morphological evidence support the elevation of <em>E</em>. <em>rotundata</em> to its own monotypic genus, <em>Pictarena</em>. The new genus <em>Pictarena</em> is defined by subsessile, suborbicular leaflets, mammiform leaflet glands, spicate inflorescences, and flowers with either all petals absent or rarely with a banner petal. Elevating <em>E</em>. <em>rotundata</em> to <em>Pictarena</em> resolves the confusing classification of the species, an imperiled endemic known only from four localities in northern Arizona and lends support for continued conservation.</p>