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gray feverfew, Gray's feverfew

guayule

Habit Biennials (sometimes flowering first year or persisting), 10–30(–60+) cm. Shrubs, 30–100+ cm.
Leaf

blades ovate or rounded-deltate to elliptic, 30–80(–120+) × 10–20(–40+) mm, usually ± pinnately or sub-bipinnately lobed, ultimate margins entire, faces strigillose, usually also with erect hairs 1–2 mm and gland-dotted.

blades lanceolate to oblanceolate, 15–25(–40+) × 6–15(–25+) mm, margins mostly entire, some with 1–2(–5) sharp teeth, faces densely strigillose (gray to white) and obscurely or not at all gland-dotted.

Peduncles

2–8(–12+) mm.

1–2(–6+) mm.

Pistillate florets

5;

corolla laminae 0 or ± coroniform, 0.1–0.5 mm.

5;

corolla laminae ovate, 1.2–1.5 mm.

Disc florets

20–30+.

20–30+.

Phyllaries

outer 5 lance-ovate to elliptic, 2.5–3+ mm, inner 5 ± orbiculate, 3–3.5 mm.

outer 5 oval-elliptic, 2.5–3+ mm, inner 5 ± orbiculate, 3.5–4 mm.

Heads

disciform or obscurely radiate, borne in open, ± paniculiform arrays.

radiate, in glomerules of 3–5+ at ends of ± ebracteate stalks 8–15(–20+) cm.

Cypselae

± obovoid, 2–3 mm; pappus-like enations 2, ± erect, deltate to ovate, 0.5–1 mm (sometimes a third, subulate spur near apex adaxially).

± obovoid, 2.5–3 mm; pappus-like enations 2(–4), erect to spreading, ± subulate, 0.3–0.8 mm.

2n

= 36, 68, 72.

= 36.

Parthenium confertum

Parthenium argentatum

Phenology Flowering Mar–Oct. Flowering Apr–Jun.
Habitat Sandy plains, openings in mesquite grasslands Calcareous soils
Elevation 20–2000 m (100–6600 ft) 1000–1500 m (3300–4900 ft)
Distribution
from FNA
AZ; NM; TX; Mexico
[WildflowerSearch map]
[BONAP county map]
from FNA
TX; Mexico
[WildflowerSearch map]
[BONAP county map]
Discussion

Guayule has sometimes been used for commercial production of natural rubber. Hybrids between Parthenium argentatum and P. incanum have been noted.

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

Source FNA vol. 21, p. 22. FNA vol. 21, p. 21.
Parent taxa Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Parthenium Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Parthenium
Sibling taxa
P. alpinum, P. argentatum, P. hysterophorus, P. incanum, P. integrifolium, P. ligulatum
P. alpinum, P. confertum, P. hysterophorus, P. incanum, P. integrifolium, P. ligulatum
Synonyms P. confertum var. divaricatum, P. confertum var. lyratum, P. confertum var. microcephalum
Name authority A. Gray: Proc. Amer. Acad. Arts 17: 216. (1882) A. Gray: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 86. (1859)
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