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riverside spineflower, Xantus' spineflower

brittle spine flower

Habit Plants erect to infrequently spreading, (0.3–)0.5–2.5(–3) × 0.5–3(–5) dm, thinly pubescent. Plants spreading to erect, 0.5–3(–5) × 0.5–3 dm, thinly pubescent, often with appressed hairs, infrequently somewhat strigose or glabrate.
Leaves

basal or nearly so;

petiole 1–2(–3) cm;

blade oblong or oblong-ovate to ovate, 0.3–1(–1.5) × 0.3–0.8(–1) cm, thinly pubescent adaxially, densely tomentose abaxially.

basal;

petiole 0.5–2 cm;

blade oblanceolate to narrowly elliptic or spatulate, (1–)1.5–3(–4) × 0.1–1 cm, pubescent.

Inflorescences

mostly flat-topped and openly branched, usually reddish;

bracts persistent, 2, usually leaflike at proximal nodes and similar to proximal leaf blades only more reduced, short-petiolate, oblong-ovate to ovate, 0.3–0.8 cm × 2–6 mm, becoming sessile, reduced and scalelike at distal nodes, linear, acicular, often acerose, 0.1–0.4 cm × 0.5–1 mm, awns straight, 0.5–1 mm.

green;

bracts 2, similar to proximal leaf blades only more reduced, 0.3–1(–1.5) cm × 1–2.5 mm, becoming sessile and scalelike at distal nodes, linear, acicular, awns 0.2–0.5 mm.

Involucres

in open clusters with 1 at node of dichotomies, reddish, cylindric, not ventricose, 3–4.5 mm, not corrugate, without scarious or membranous margins, thinly to densely pubescent;

teeth spreading, unequal, 0.7–1.5 mm, 3 longer ones more erect than 3 shorter and less-prominent ones;

awns uncinate, 0.5–1 mm.

1, green, 3–5 mm, not corrugate, thinly strigose;

teeth divergent, 0.4–1.2 mm;

awns uncinate, 0.2–0.5 mm.

Flowers

long-exserted;

perianth rose to red, infrequently with white lobes, cylindric, 4.5–6 mm, pubescent;

tepals connate ca. 2/3 their length, monomorphic to slightly dimorphic, narrowly oblanceolate, rounded apically, those of outer whorl occasionally slightly broader and longer than those of inner whorl;

stamens 9, mostly included;

filaments distinct, 4–6 mm, glabrous;

anthers pink to red, oblong, 0.5–0.6 mm.

included;

perianth greenish white to white or pale yellowish white, cylindric, 2–4 mm;

tepals connate 3/4 their length, monomorphic, linear to narrowly oblanceolate, acute, entire apically;

stamens slightly exserted;

filaments distinct, 2–3.5 mm, glabrous;

anthers white to pale yellow, ovate, 0.3–0.4 mm.

Achenes

brown, lenticular, 4–4.5 mm.

dark brown, lenticular, 3–4 mm.

Chorizanthe xanti

Chorizanthe brevicornu

Distribution
from FNA
CA
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from FNA
AZ; CA; ID; NV; OR; nw Mexico
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[BONAP county map]
Discussion

Varieties 2 (2 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Varieties 2 (2 in the flora).

Chorizanthe brevicornu has stems and branches that easily disarticulate at the nodes. Dried specimens often are reduced to a mere jumble without careful handling. The vegetative fragments will not regenerate new plants, but the involucres (each with a single flower bearing a single achene) easily disarticulate from the parent plant, and with the aid of the awns on the teeth of the involucre, may be readily distributed.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Involucres thinly pubescent
var. xanti
1. Involucres densely white-pubescent
var. leucotheca
1. Leaf blades oblanceolate to narrowly elliptic, 0.1-0.3(-0.5) cm wide; involucres prominently ribbed at maturity; Mojave and Sonoran deserts
var. brevicornu
1. Leaf blades broadly oblanceolate to broadly spatulate, 0.5-1 cm wide; involucres obscurely ribbed at maturity; Great Basin Desert and Snake River Plains
var. spathulata
Source FNA vol. 5, p. 463. FNA vol. 5, p. 469.
Parent taxa Polygonaceae > subfam. Eriogonoideae > Chorizanthe > subg. Amphietes > sect. Ptelosepala Polygonaceae > subfam. Eriogonoideae > Chorizanthe > subg. Amphietes > sect. Fragile
Sibling taxa
C. angustifolia, C. biloba, C. blakleyi, C. brevicornu, C. breweri, C. clevelandii, C. corrugata, C. cuspidata, C. diffusa, C. douglasii, C. fimbriata, C. howellii, C. leptotheca, C. membranacea, C. obovata, C. orcuttiana, C. palmeri, C. parryi, C. polygonoides, C. procumbens, C. pungens, C. rectispina, C. rigida, C. robusta, C. spinosa, C. staticoides, C. stellulata, C. uniaristata, C. valida, C. ventricosa, C. watsonii, C. wheeleri
C. angustifolia, C. biloba, C. blakleyi, C. breweri, C. clevelandii, C. corrugata, C. cuspidata, C. diffusa, C. douglasii, C. fimbriata, C. howellii, C. leptotheca, C. membranacea, C. obovata, C. orcuttiana, C. palmeri, C. parryi, C. polygonoides, C. procumbens, C. pungens, C. rectispina, C. rigida, C. robusta, C. spinosa, C. staticoides, C. stellulata, C. uniaristata, C. valida, C. ventricosa, C. watsonii, C. wheeleri, C. xanti
Subordinate taxa
C. xanti var. leucotheca, C. xanti var. xanti
C. brevicornu var. brevicornu, C. brevicornu var. spathulata
Name authority S. Watson: Proc. Amer. Acad. Arts 12: 272. (1877) Torrey: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 177. (1859)
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