Because they share several morphological and ecological characters, the North American sparrow (Emberizidae) genera Ammodramus, Passerculus, and Xenospiza have historically been considered members of a well-defined “grassland” sparrow assemblage. Relationships among the 11 members of this group have been the subject of much taxonomic debate, yet no comprehensive molecular assessment of relationships has been done. We investigated these relationships using mitochondrial DNA sequence data that included complete cytochrome-b and ND2 genes. Phylogenetic reconstructions derived via parsimony, likelihood, and Bayesian methods were congruent. The grassland sparrows, as presently configured, are polyphyletic. Pooecetes gramineus, Amphispiza belli (but not A. quinquestriata and A. bilineata), Oriturus superciliosus, and all three species of Melospiza are included in a reconfigured clade, whereas the traditional forms of Ammodramus savannarum, humeralis, and aurifons are placed well outside of these. Within the clade of interest, Ammodramus remains polyphyletic, with leconteii, maritimus, nelsoni, and caudacutus forming a well-resolved clade apart from henslowii and bairdii. The latter are in another strongly supported clade that also includes Passerculus and a Xenospiza-Melozpiza sister pairing. Pooecetes, Amphispiza (belli), and Oriturus represent early lineages in this clade that today have no close living relatives. The polyphyly of the genus Ammodramus is likely the result of morphological convergence attributable to similar adaptive responses to the occupation of similar habitats. In general, the morphological and ecological factors that have defined the grassland sparrows are poor indicators of relatedness. Taxonomic revisions are suggested.
Evaluación Molecular del Clado de Gorriones de Pastizales de Norte América