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

Errazurizia (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 E. rotundata 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 Errazurizia 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 E. rotundata was sister to the monotypic genus Parryella. Gland and pollen surface characters confirm the close relationship between P. filifolia and E. rotundata. Cytonuclear discordance yielded partially incongruent tree topologies, and while the cpDNA phylogeny indicated a monophyletic Amorpha was sister to the E. rotundata and P. filifolia clade, the nrDNA cistron phylogeny recovered a paraphyletic Amorpha, with A. californica sister to the E. rotundata and P. filifolia clade. Molecular and morphological evidence support the elevation of E. rotundata to its own monotypic genus, Pictarena. The new genus Pictarena 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 E. rotundata to Pictarena resolves the confusing classification of the species, an imperiled endemic known only from four localities in northern Arizona and lends support for continued conservation.