Ambrosia confertiflora DC.

Perennials, 20–80(–150+) cm. Stems erect. Leaves mostly alternate; petioles 10–35 mm; blades lanceolate to ovate, 40–85(–150) × 20–35(–55) mm overall, lacini­ately 2–4-pinnately lobed (lobes ± lanceolate); bases cuneate to truncate, ultimate margins entire, abaxial and adaxial faces strigillose to sericeous (often grayish) and gland-dotted. Pistillate heads clustered, proximal to staminates; florets 1(–2). Staminate heads: peduncles 0.5–2 mm; involucres cup-shaped, 1.5–3+ mm diam., strigillose; florets 5–20+. Burs: bodies pyramidal to pyriform, 1–2 mm, strigillose to pilosulous, spines (1–)5–12+, mostly distal, stoutly conic to subulate, 0.5–1 mm, tips uncinate. 2n = 72, 108.

Franseria confertiflora (de Candolle) Rydberg

Franseria strigulosa Rydberg, sp. no v
A perennial herb; stem 3-6 dm. high, striate, strigulose or with a few coarser hairs; lower leaves 1-1.2 dm. long, bipinnatifid or tripinnatifid, softly grayish-strigulose on both sides, short-petioled, obovate in outline; segments oblong or linear-oblong, obtusish, or the terminal one lanceolate and longer; upper leaves less dissected; inflorescence a leafy panicle; staminate . heads short-peduncled, nodding; involucre 2.5-3 mm. broad, sparingly strigulose; lobes 6-8, triangular; paleae of the receptacle filiform, slightly clavate at the apex, sparingly glandularpuberulent and sparingly hispid at the tip; pistillate heads in small clusters on the lower part of the branches; fruit about 3 mm. long, pubescent and .glandular-granuliferous, reticulateridged, 1 -flowered; beak solitary, subulate-conic; spines 16-20, conic-subulate below, hooked at the apex.
Type collected in Los Angeles County, California, September 1899, L. T. Chamberlain (herb. N. Y. Bot. Gard.).
Distribution: Southern California, Lower California, Sonora, and Sinaloa.

Franseria confertiflora (DC.) Rydb
Ambrosia fraticosa DC. Prodr. 5: 525. 1836. Not Ambrosia fruticosa Medic. 1775. Ambrosia confertiflora DC. Prodr. 5: 526. 1836.
A perennial herb, 3-20 dm. high, in the south sometimes becoming woody at the base, very leafy and branched; stem appressed-hispid; leaves bipinnately or tripinnately and interruptedly dissected, short-petioled, strigose-hispidulous on both sides, 5-15 cm. long; segments linear or linear-oblong, acute, the terminal ones elongate; heads in more or less leafy panicles, the staminate ones numerous, reflexed on spreading peduncles, which are 1-2 mm. long; involucre turbinate-hirsutulous and glandular-puberulent, 2-2.5 (rarely 3) mm. broad, irregularly lobed; lobes 8-10, broadly triangular, ciliolate; paleae of the receptacle filiform, with spatulate pubescent tips; corolla pubescent; teeth triangular; pistillate heads in small clusters in the upper axils and on the lower part of the staminate racemes, 1-2-flowered; fruit ovoid, 2-3 mm. long, glandular-puberulent; beak single, conic, incurved at the apex; spines 6-18, connected by ridges, somewhat dilated below, more or less hooked at the apex, each with a reticulate pit or areola above its base.
Type locality: Matamoros, Tamaulipas.
Distribution: Tennessee; from Oklahoma and southern Colorado to Arizona, Sinaloa, and Tamaulipas.

Ambrosia confertiflora is a North American species of ragweed known by the common name weakleaf bur ragweed.

Ambrosia confertiflora là một loài thực vật có hoa trong họ Cúc. Loài này được DC. mô tả khoa học đầu tiên năm 1836.