The flowers of penstemon whippleanus
are colored a particularly rich, reddish shade of purple and borne in clusters at the top of the stem and the upper few leaf nodes. Occasionally the corolla can be pale blue or white. Flowers in each cluster are arranged in a ring, pointing in all directions, angled slightly downwards. The flowers, the long, thin leafy bracts underneath and the upper part of the stem are covered by short glandular hairs, but the lower part of the stem is smooth and hairless. Longer hairs are found on the interior of the lower, three-lobed lip, which projects forwards and does not curve back to any great degree. The upper lip bends slightly upwards.
Leaves grow in opposite pairs at quite widely-spaced intervals, all along the stem. The plant is a late blooming species, brightening up the high mountains until early autumn.