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. 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.
