As is the case for most species in the genus Spinus, lesser goldfinch males have a black forehead, which females lack.

[11] There is a slight northwest-southeast cline in size, with the largest birds from Mexico and further south being up to one-fifth larger than the smallest from the extreme northwest of its range; this effect is more pronounced in females.

[8] Males are easily recognized by their bright yellow underparts and big white patches in the tail (outer rectrices) and on the wings (the base of the primaries).

[8] The zone in which both light and dark males occur on a regular basis is broadest in the north and extends across the width of the Rocky Mountains and the Sierra Madre Occidental ranges.

It reaches the Pacific Coast in southern Sonora to northern Sinaloa, roughly between the area of Ciudad Obregón to Culiacán.

This subspecies, as well as the even yellower S. p. jouyi from the Yucatán Peninsula and adjacent regions of Mexico and S. p. witti from the Tres Marías Islands off Nayarit[14] require more study, especially since at least the former two also seem to be significantly larger and longer-billed.

They are best distinguished from other members of the genus by the combination of small size, upperparts without white or yellow, and dark gray bill.

It utilizes almost any habitat with trees or shrubs except for dense forest, and is common and conspicuous in many areas, often coming near houses.

[17] The nesting season is in summer in the temperate parts of its range; in the tropics it apparently breeds all-year round, perhaps less often in September and October.

[18] It lays three or four bluish white eggs in a cup nest made of fine plant materials such as lichens, rootlets, and strips of bark, placed in a bush or at low or middle levels in a tree.