It appears that what Russo refers to as the "small thorn or bristle" of the T. howardii gall rises slim and untapered from a basically spherical surface divided into "plates." By contrast, the "bristle" of the Contarinia gall gradually tapers from a fleshy base that is itself tapered. To complicate matters further, the two galls may occur right next to each other.

Galls have been found in Arizona, southern California, and Nevada, including a Nevada gall reported on BugGuide.