Parthenium incanum
Parthenium argentatum
mariola
guayule
blades oval-elliptic to obovate, 15–25(–40+) × 6–15(–25+) mm, sometimes pinnately (3–)5–7-lobed or round-toothed, ultimate margins entire, faces tomentose (gray to white) 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.
1–3+ mm.
1–2(–6+) mm.
5;
corolla laminae ovate, 1–1.5 mm.
5;
corolla laminae ovate, 1.2–1.5 mm.
8–20(–30+).
20–30+.
outer 5 oblong, 1.5–2 mm, inner 5 orbiculate, 2–2.5 mm.
outer 5 oval-elliptic, 2.5–3+ mm, inner 5 ± orbiculate, 3.5–4 mm.
radiate, in glomerules of 3–5+ on branched stalks 1–5(–12+) cm, forming compound, corymbiform arrays.
radiate, in glomerules of 3–5+ at ends of ± ebracteate stalks 8–15(–20+) cm.
obovoid, 1.5–2 mm; pappus-like enations 2(–3), erect to spreading, ± subulate, 0.5–1 mm.
± obovoid, 2.5–3 mm; pappus-like enations 2(–4), erect to spreading, ± subulate, 0.3–0.8 mm.
= 54.
= 36.
Parthenium incanum
Parthenium argentatum
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.)
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