Penstemon xylus
Bot. Gaz. 34: 31. 1902. (as Pentstemon)
Stems prostrate, spreading, or ascending, 6–12 cm, retrorsely hairy, hairs pointed, sometimes also appressed, white, scalelike. Leaves not leathery, glabrous or sparsely hairy, hairs appressed, white, scalelike abaxially, ± densely hairy, hairs appressed, white, scalelike adaxially; cauline 1–5 pairs, petiolate, 6–16 × 2–4.5 mm, blade obovate to spatulate, base tapered, apex rounded to mucronate or acute. Thyrses continuous, secund, 2–12 cm, axis retrorsely hairy, hairs appressed or spreading, white, scalelike, sometimes also glandular-pubescent distally, verticillasters 3–12, cymes 1–3(or 4)-flowered, 1 per node; proximal bracts spatulate to oblanceolate, 8–17 × 1.4–4 mm; peduncles and pedicels spreading to ascending, glandular-pubescent, hairs appressed, white, scalelike. Flowers: calyx lobes lanceolate to oblong, 3–5 × 0.7–1 mm, herbaceous-margined, glandular-pubescent and retrorsely hairy, hairs appressed, white, scalelike; corolla blue to lavender, or violet, lined internally abaxially with reddish violet nectar guides, ampliate, 12–18 mm, yellow-lanate internally abaxially, tube 5–6 mm, throat gradually inflated, 3.5–5 mm diam., 2-ridged abaxially; stamens reaching orifice or longer pair exserted, filaments glabrous, pollen sacs opposite, navicular to subexplanate, 0.6–0.8 mm, sutures papillate; staminode 7–8 mm, included, flattened distally, 0.2–0.3 mm diam., tips straight to recurved, distal 6–7 mm pubescent, hairs yellow or orange, to 0.7 mm; style 11–14 mm. Capsules 3–5 × 3–4 mm.
Phenology: Flowering Jun–Aug.
Habitat: Sandy or gravelly slopes, sagebrush shrublands, aspen woodlands, pine woodlands.
Elevation: 2100–3100 m.
Discussion
Penstemon xylus is known from south-central Utah. Populations are documented in Beaver, Garfield, Iron, Piute, and Sevier counties. The placement of P. xylus remains unclear. D. D. Keck (1937) treated it as P. caespitosus subsp. suffruticosus. N. H. Holmgren (1979b) believed it to be more closely related to P. thompsoniae, which also has vestiture of appressed, white, scalelike hairs.
The correct name for Penstemon xylus at the rank of species, which has been a source of confusion, was discussed by C. C. Freeman (2017).
Selected References
None.