All parts of penstemon centranthifolius
are smooth and hairless; the grey-green leaves, the purplish stems, the green to purple calyces and the bright red flowers. Leaves are quite thick, often curved up along the axis, and those around the middle of the stem are the longest; up to 4 inches. Leaves are stalkless, their bases slightly clasping the stem.
The calyx is about a quarter of an inch long, divided into five broadly ovate lobes, while the tubular corolla is much longer, one inch or more. This opens only at the tip into five small lobes, which stay projecting forwards, not spreading, hence the four stamens and the one infertile stamen (which is also hairless) remain largely hidden. Flowers are usually arranged on all sides of the stem, which grows upright. The pedicels point upwards, while the flowers hang down. The elongated flower cluster is quite extensive, occupying up to 2 feet of the stem.