Flowers of justicia longii
are slender, and not so noticeable; the white corolla is a narrow tube up to 1.5 inches long, with small leaves at the base, and opening to an upper lip and a lower lip. The lower lip is partly divided into three lobes, and bent backwards by about 90 degrees, while the upper lip is undivided, though slightly notched to the tip, projecting forwards or also recurved. Flowers tend to bloom for short times, often opening in the evening and withering by the following afternoon. They form at the leaf nodes, singly or in small clusters.
Leaves, stems and the outside of the corolla have a very fine covering of short, pubescent hairs. Stems are somewhat woody towards the base. Plants are found across southern Arizona, and (uncommonly) in a small area of Presidio county, west Texas.