(Pallas ex Pursh) G. L. Nesom & G. I. Baird, Phytologia. 75: 84. 1993.
Pallas ex Pursh, Fl. Amer. Sept. 2: 517. 1813;
(Pallas ex Pursh) Britton
erect or ascending to spreading, white to green, fastigiately branched, tomentose.
(usually crowded) usually ascending to spreading; blades filiform to narrowly oblanceolate (mostly adaxially sulcate to concave), 10—70 × 0.3—10 mm, midnerves mostly evident, apices acute, faces glabrous or tomentose, often gland-dotted (lacking well-defined circular pits)
axillary fascicles absent.
in rounded to flat-topped, cymiform arrays (to 12 cm wide).
1—20 mm (bracts usually 0, sometimes 1—5, reduced, scalelike).
obconic to subcylindric, 6—16 × 2—4 mm.
10—31 in 3—5 series (often in vertical ranks), tan, ovate to lanceolate, 1.5—14 × 0.7—1.5 mm, strongly unequal, mostly chartaceous (mostly keeled), midnerves raised for nearly entire lengths, expanded apically, apices acute to obtuse, abaxial faces resinous.
(4—)5(—6); corollas 6—12 mm.
tan, turbinate to cylindric or oblanceoloid, 3—8 mm, glabrous or hairy (often ± pilose or sericeous);
whitish, 3—13 mm.
Varieties 21 (21 in the flora): w North America, nw Mexico.
is widespread, often abundant, and complex. This treatment is based largely on that by L. C. Anderson (1986b). Uncertainty about the specimen used by Pursh to establish
) is a possible source of confusion concerning the application of that name (which is in current use) and of the name
Nuttall (J. L. Reveal et al. 1999). Anderson divided the species into two informal groups, the "green forms" and the "gray forms." These two groups were formalized as subspp.
by G. L. Nesom and G. I. Baird (1993), each containing varieties.
is reported to hybridize with other species in the genus, and hybrid and formula names have been applied to them. Their synonymies were more fully summarized by Nesom and Baird.
(A. Gray) G. L. Nesom & G. I. Baird, based on
A. Gray is the hybrid between
(L. C. Anderson and J. L. Reveal 1966).
(L. C. Anderson) G. L. Nesom & G. I. Baird, "Uinta rubber rabbitbrush," based on
L. C. Anderson, is the hybrid between
(L. C. Anderson 1984).
(D. D. Keck) G. L. Nesom & G. I. Baird, based on
D. D. Keck, is the hybrid between
(L. C. Anderson 1986b).
Anderson, L. C. 1986b. Sympatric subspecies in
. In: E. D. McArthur and B. L. Welch, eds. 1986. Proceedings, Symposium on the Biology of
, Provo, Utah, July 9—13, 1984. Ogden. Pp. 98—103. Ostler, W. K., C. M. McKell, and S. White. 1986.
: A potential source of natural rubber. In: E. D. Mc Arthur and B. L. Welch, eds. 1986. Proceedings, Symposium on the Biology of
, Provo, Utah, July 9—13, 1984. Ogden. Pp. 389—395.