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.
Heads radiate, the rays 7-12, pistillate and fertile; invol bracts strongly imbricate, glutinous, shining, with stramineous base and abrupt green tip; receptacle flattish or convex, alveolate and sometimes also pubescent; disk-fls 10-50, functionally staminate, without an ovary, the style-branches short, slender, short-hairy, not stigmatic; achenes clavate, hairy; pappus of the disk-fls of 5(-8) long, white, spatulate scales united to half-length, that of the rays a minute, toothed crown or several short, ±concrescent scales; taprooted, glabrous annuals with alternate, narrow, entire, punctate lvs and numerous small yellow heads in a ±flat-topped infl. 2, N. Amer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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