(de Candolle) Nuttall

Trans. Amer. Philos. Soc., n. s. 7: 313. 1840

Common names: Broomweed
Etymology: Greek amphi -, around, and achyron, chaff or husks, alluding to ring of pappus elements
Basionyms: Brachyris sect. Amphiachyris de Candolle
Treatment appears in FNA Volume 20. Treatment on page 87. Mentioned on page 9, 88, 89, 95.
Annuals, 20–100(–200) cm (glabrous, with strong terpenoid smell when crushed; taprooted). Stems erect, usually branched distally (bases usually lignescent). Leaves cauline; alternate; sessile; blades (1- or 3-nerved) linear to lanceolate, margins entire, faces gland-dotted. Heads radiate, in paniculiform or corymbiform arrays. Involucres narrowly campanulate to turbinate, 2–4 mm diam. Phyllaries 12–15 in 1–2(–3) series, 1-nerved (nerves without green margins) ovate, unequal, proximal 2/3 indurate, margins hyaline, faces whitish resinous. Receptacles flat to slightly convex, smooth (glabrous or hairy with multicellular, 1-seriate hairs), epaleate. Ray florets 7–12, pistillate, fertile; corollas yellow, sometimes drying orange-tinged. Disc florets 10–21, functionally staminate; corollas yellow, tubes shorter than cylindric throats, lobes 5, erect, deltate; style-branch appendages fused (pappi of 5–8 white, basally connate, linear, spatulate-tipped scales in 1 series, ± equaling corollas). Cypselae (ray, purplish black) obovoid-turbinate, plump, 4–9-ribbed (apices attenuate to slightly clavate), faces densely long- or short-setulose (hairs appressed, white), mostly occurring in lines between ribs; pappi coroniform. x = 4, 5.


c United States.


Species 2 (2 in the flora).

Amphiachyris was recently treated within a more inclusive Gutierrezia (G. M. Diggs et al. 1999); apparently, it is more closely related to monotypic Thurovia than to Gutierrezia (Y. Suh and B. B. Simpson 1990). Amphiachyris is distinguished from Gutierrezia by a combination of glandular hairs only on the abaxial leaf faces, functionally staminate disc florets, disc pappi of basally connate, narrowly spatulate scales ± equaling corollas, and abaxial nerves of the phyllaries without green borders.

Lower Taxa


1 Plants 20–40(–60) cm; heads in open paniculiform arrays; cypselae 4–6-ribbed, long-setulose; leaf blades 0.2–1(–2) mm wide; receptacles with hooked, swollen-based hairs Amphiachyris amoena
1 Plants 30–100(–200) cm; heads in crowded corymbiform arrays; cypselae 7–9-ribbed, short-setulose; leaf blades 0.5–6 mm wide; receptacles glabrous Amphiachyris dracunculoides