Flowers of penstemon ambiguus
are somewhat atypical for this genus, as the corolla is not so obviously bi-lipped, but instead more symmetric, with five similar lobes approximately at right-angles to the tube, though the upper two are a little smaller than the lower three, and angled slightly further backwards. The corolla tube, around an inch long, is pink, the lobes paler pink to almost white. The inside of the tube is crossed by dark pink nectar lines. Calyces are small, enclosing only the very lower end of the corolla tube, and are divided to the base into five ovate lobes. The four stamens and the one staminode (infertile stamen) are included within the tube.
Plants are branched, bushy subshrubs, almost 2 feet high, producing dozens of stems. Leaves are linear, very narrow, with rough edges and pointed tips. Flowers form in small, open clusters at the branch tips.