Biennials (sometimes flowering first year or persisting), 10-30(-60+) 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. Heads disciform or obscurely radiate, borne in open, ± paniculiform arrays. Peduncles 2-8(-12+) mm. Phyllaries: outer 5 lance-ovate to elliptic, 2.5-3+ mm, inner 5 ± orbiculate, 3-3.5 mm. Pistillate florets 5; corolla laminae 0 or ± coroniform, 0.1-0.5 mm. Disc florets 20-30+. 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). 2n = 36, 68, 72.

Flowering Mar-Oct. Sandy plains, openings in mesquite grasslands; 20-2000 m; Ariz., N.Mex., Tex.; Mexico.

Duration: Biennial

Nativity: Native

Lifeform: Forb/Herb

General: Biennial or perennial herbs, sometimes flowering first year, 10-60 cm tall; stems one to few from the base, branching above, longitudinally striate and densely hirsute with long hairs. 

Leaves: Alternate along the stems, the lower leaves subpetiolar and upper leaves sessile; blades ovate or rounded-deltate to elliptic in outline, 3-12 cm long and 2-4 cm wide, pinnately or sub-bipinnately lobed, the ultimate margins entire; leaf surfaces strigillose, usually also gland-dotted and with erect hairs 1-2 mm long.

Flowers: Flower heads disciform or obscurely radiate, small, white and inconspicuous, borne in open terminal panicles, on peduncles 2-12 mm long; involucres broadly cup-shaped, the bracts (phyllaries) in 2 series: outer series of 5 lance-ovate to elliptic phyllaries, 3 mm long; inner series of 5 orbiculate phyllaries, 3 mm long; pistillate (ray) florets 5 per flower head, the laminae (ray petals) white, less than 0.5 mm long or lacking; disc florets 20-30 per flower head, white. 

Fruits:  Achenes obovoid, 2-3 mm long; topped with a pappus of 2 scales, these less than 1 mm long.

Ecology: Found on sandy plains, in openings in mesquite grasslands, pinyon-juniper woodlands, desertscrub, and canyon bottoms, below 6,000 ft (1829 m); flowers March-October.

Distribution: se AZ, s NM, and sw TX; south to nw MEX.

Notes: P. confertum looks like a smaller, herbaceous version of the common shrub Parthenium incanum. Look for the lobed gray-colored leaves, the striate stems covered with long hairs, and the terminal panicle of small white flower heads that may or may not have a few minute ray petals. Material from Arizona and New Mexico is traditionally assigned to var. lyrata, although the Flora of North America does not distinguish among the different varieties.

Ethnobotany: Unknown; however, other species in the genus have uses.

Etymology: Parthenium is from the Greek parthenos, virginal or pure, alluding to the white flowers; confertum is Latin for crowded, probably referring to the crowded sessile leaves on the middle and upper stems.

Synonyms: Parthenium lyratum

Editor: AHazelton 2017

Parthenium confertum var. lyratum is not woody like Parthenium incanum, but rather herbaceous and bright green in appearance rather than grayish. The lobed leaves of Parthenium confertum var. lyratum are larger than those of Parthenium incanum as well. The flowers of the two species look similar though, with about 5 widely spaced short white ray flowers and a woolly appearing white disc. The achene is glabrous, rather than pubescent as with Parthenium incanum. Parthenium confertum var. lyratum is found on rocky slopes at middle elevation.