The Rufous-rumped Seedeater is a small bird whose male has a gray head and back with chestnut throat and underparts. In Argentina, it breeds in tall, humid grassland.
The male has a gray crown, nape, and back, with chestnut throat, flanks, rump, and belly; its black wings and tail have white patches. The female is olive-brown above and ochre below.
In Argentina, it is associated with tall, humid grassland and nests there.
An extinction-risk assessment has not been added yet.