Dictionary:

penstemon

  (pĕn-stē'mən, pĕn'stə-mən)

Any of numerous plants of the genus Penstemon, native to North America and eastern Asia, having opposite leaves, flowers with a usually two-lipped, variously colored corolla, and capsules containing many seeds. Also called beardtongue.

[New Latin Pēnstēmōn, genus name : Greek pente, five + Greek stēmōn, thread.]

A North American genus of plants in the family Scrophulariaceae which act as facultative selenium converters; the selenocompounds produced by the plant cause alopecia, lameness, laminitis; called also beard tongue.

Pen-stee'mon. Beardtongue . A large genus of 250 species of herbs, rarely shrubs, chiefly from the w. U.S. Many of the species are important bee plants in the West.

Description
Leaves opposite or whorled, and showy. Flowers 2-lipped, tubular, mostly in terminal racemes or panicles. Calyx 5-parted. Corolla with the lower lip 3-lobed, the upper lip 2-lobed. Stamens 5, with 4 fertile, the fifth sterile and often bearded.

How to Grow
Start seeds indoors in very early spring. Seeds need light for germination and sprout slowly and unevenly. Transplant outdoors after last frost. Well-drained, enriched soil, with a pH 6.5-7.0, produces the best results. Grow in full sun in cool climates, but give afternoon shade where summers are long and hot. Plants prefer cool weather.

Penstemon gloxinioides
Penstemon . 2-3 ft. (60-90 cm) high. Flowers 2 in. (5 cm) wide, bell-shaped with flared lip, colors ranging from white to crimson and blue. Mexico. This hybrid derives from P. Hartwegii and P. Cobaea . Much grown on the West Coast. Half-hardy annual.

The botanical name for beard-tongue.

The noun has one meaning:

Meaning #1: large genus of subshrubs or herbs having showy blue or purple or red or yellow or white flowers; mostly western North America
  Synonym: genus Penstemon