Shrubs, 30-100+ cm. Leaf 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. Heads radiate, in glomerules of 3-5+ on branched stalks 1-5(-12+) cm, forming compound, corymbiform arrays. Peduncles 1-3+ mm. Phyllaries: outer 5 oblong, 1.5-2 mm, inner 5 orbiculate, 2-2.5 mm. Pistillate florets 5; corolla laminae ovate, 1-1.5 mm. Disc florets 8-20(-30+). Cypselae obovoid, 1.5-2 mm; pappus-like enations 2(-3), erect to spreading, ± subulate, 0.5-1 mm. 2n = 54.
Flowering (May-)Jul-Nov. Openings in desert scrub, often on limestone soils; 1000-1500 m; Ariz., Nev., N.Mex., Tex., Utah; Mexico.
Common Name: mariola
Duration: Perennial
Nativity: Native
Lifeform: Shrub
General: Much branched, compact shrub, 30-100 cm tall, with finely tomentose herbage and light gray, striate, eventually slightly fissured bark.
Leaves: Alternate along the branches, on tomentulose petioles 2-5 mm long; blades oval-elliptic to obovate in outline, 2 cm long by 6-15 mm wide, irregularly lobed or pinnatifid, the lobes obtuse to rounded, 5-10 cm long; lower leaf surface densely tomentose, pale or ashy green, and veiny; upper leaf surface less tomentose and veiny.
Flowers: Flower heads radiate but small, white, and not particularly showy, arranged in terminal cymose panicles set well above the leaves on naked or nearly naked branches 1-5 cm long; involucres broadly cup shaped, 3-5 mm wide at anthesis, the bracts (phyllaries) in several graduated series, ovate to suborbicular, tomentulose; ray florets 5 per flower head, white, the laminae (ray petals) 1-2 mm long, only slightly exceeding involucres, mostly erect or weakly spreading; disc florets 8-20 per flower head, sterile, 2 mm high, white.
Fruits: Achenes 2 mm long, hairy, dorsiventrally flattened, attached to its subtending receptacle bract and the bracts of 2 sterile disk flowers immediately anterior to it by slender callous threads.
Ecology: Found on gravelly slopes and plains from 2,500-5,000 ft (762-1524 m); flowers June-October.
Distribution: s NV, s UT, AZ, NM and sw TX; south to s MEX.
Notes: Distinctive as a mostly low-growing, gray-green shrub with a strong scent (pleasant to some); tomentose foliage; small, lobed leaves; and cream colored, cup-shaped flower heads with a few ray florets that are folded at the base and notched at the tip, sometimes resembling hearts. Can be common or dominant in Chihuahuan desert scrub and grasslands, and on limestone in other deserts. It is closely related to guayule (Parthenium argentatum) a northern Mexican species cultivated for its natural rubber content. P. incanum is said to contain a small amount of rubber as well and can hybridize with P. argentatum where their ranges overlap.
Ethnobotany: The leaves were boiled and drunk like coffee; also used medicinally by the Jicarilla Apache.
Etymology: Parthenium is from the Greek parthenos, virginal or pure, alluding to the white flowers; incanum means grayish or hoary.
Synonyms: None
Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2017
