Penstemon sect. Caespitosi

(Rydberg) Pennell

Contr. U.S. Natl. Herb. 20: 327, 334. 1920.

Basionym: Penstemon [unranked] Caespitosi Rydberg Fl. Colorado, 306. 1906
Treatment appears in FNA Volume 17. Treatment on page 98. Mentioned on page 93, 105, 207.

Subshrubs, usually cespitose. Stems retrorsely hairy, rarely glabrous, not glaucous. Leaves cauline, rarely basal and cauline (P. retrorsus), opposite, leathery or not, glabrous, glabrate, pubescent, scabrous, puberulent, or retrorsely hairy, not glaucous; basal and proximal cauline petiolate; cauline petiolate or sessile, blade obovate, spatulate, oblanceolate, lanceolate, elliptic, or linear, margins entire. Thyrses continuous or interrupted, cylindric or secund, axis retrorsely hairy, glandular-pubescent, or puberulent and glandular-pubescent, rarely glabrous, cymes 1 or 2 per node; peduncles and pedicels spreading to ascending or erect. Flowers: calyx tube 0.2–1 mm (1.5–2 mm in P. retrorsus), lobes: margins entire or erose, ± scarious or herbaceous, glandular-pubescent or retrorsely hairy, rarely glabrate; corolla lavender, blue, violet, or purple, rarely scarlet, bilaterally symmetric, bilabiate, not personate, funnelform, tubular-funnelform, salverform, ventricose-ampliate, or ampliate, glandular-pubescent externally, hairy internally abaxially, rarely glabrous, throat slightly to abruptly inflated, not constricted at orifice, 2-ridged abaxially; stamens included to exserted, filaments glabrous, rarely sparsely glandular-puberulent proximally, pollen sacs opposite, rarely divergent, navicular to subexplanate or explanate, dehiscing completely, connective splitting, sides glabrous, sutures papillate or smooth; staminode included to exserted, ± flattened distally, 0.1–0.5 mm diam., tip straight to recurved, distal (20–)50–100% hairy, hairs to 0.7–1.3 mm; style glabrous. Capsules glabrous. Seeds dark brown to black, angled to rounded, 1.1–2.1 mm.


w United States, nw Mexico.


Species 11 (11 in the flora).

Most species of sect. Caespitosi formed a clade in the molecular study by A. D. Wolfe et al. (2006); placement of the clade within subg. Penstemon is not clear.


1 Corollas salverform, scarlet (throats sometimes yellow or yellow- or orange-spotted). Penstemon pinifolius
1 Corollas tubular-funnelform, funnelform, ampliate, or ventricose-ampliate, lavender, blue, violet, or purple. > 2
2 Leaves glabrous or retrorsely hairy, hairs appressed, white, scalelike. > 3
3 Stems prostrate, spreading, or ascending; cauline leaves 1–5 pairs. > 4
4 Leaves densely retrorsely hairy, hairs appressed, white, scalelike; pollen sacs 0.8–1.2(–1.4) mm; Arizona, California, Nevada, Utah. Penstemon thompsoniae
4 Leaves glabrous or sparsely hairy, hairs appressed, white, scalelike abaxially, ± densely hairy, hairs appressed, white, scalelike adaxially; pollen sacs 0.6–0.8 mm; Utah. Penstemon xylus
3 Stems ascending to erect; cauline leaves 6–30 pairs. > 5
5 Leaves glabrous, rarely sparsely retrorsely hairy, hairs white, scalelike abaxially, densely puberulent, hairs white, scalelike adaxially; corollas 9–14 mm; pollen sacs 0.5–0.8 mm; Arizona. Penstemon discolor
5 Leaves sparsely to densely retrorsely hairy, hairs appressed, white, scalelike; corollas 14–20 mm; pollen sacs 0.9–1.4 mm; Arizona, California, New Mexico. > 6
6 Corollas tubular-funnelform, 14–18 mm, purple to violet; California. Penstemon californicus
6 Corollas ventricose-ampliate, 16–20 mm, blue to lavender; Arizona, New Mexico. Penstemon linarioides
2 Leaves glabrous, glabrate, or hairy, hairs pointed. > 7
7 Calyx tubes 1.5–2 mm; proximal bracts oblanceolate. Penstemon retrorsus
7 Calyx tubes 0.2–1 mm; proximal bracts oblanceolate to linear. > 8
8 Calyx lobes herbaceous- or narrowly scarious-margined. > 9
9 Stems and leaves not cinereous; leaf blades obovate to spatulate, oblanceolate, or linear; Arizona, Colorado, Utah, Wyoming. Penstemon caespitosus
9 Stems and leaves cinereous; leaf blades linear; Colorado. Penstemon teucrioides
8 Calyx lobes broadly scarious-margined. > 10
10 Corollas ventricose-ampliate; calyx lobe apices acute to acuminate. Penstemon linarioides
10 Corollas funnelform; calyx lobe apices acuminate to caudate. > 11
11 Leaf blades linear, rarely oblanceolate; stems ascending to erect; corollas glabrous or sparsely white-villous internally abaxially; Utah. Penstemon abietinus
11 Leaf blades elliptic to obovate, oblanceolate, or linear; stems prostrate, decumbent, ascending, or erect; corollas sparsely to densely yellow-lanate or yellow-pilose internally abaxially; Colorado, New Mexico, Utah. Penstemon crandallii