virgatus or Penstemon unilateralis
is a tall plant with blossoms concentrated on one side of the stem, as described
by the species name unilateralis. Leaves are long and narrow. The staminode,
or non-functional stamen, of P. unilateralis is white and hairless.
Compare to Penstemon secundiflorus,
which also has flowers toward one side of the stem. P. secundiflorus
has a hairy staminode and broader, grayer leaves.