Index Seminum (Bratislave) 1837: [3]. 1837.

Etymology: Greek achyron, scale, and Latin achaenium, fruit, alluding to cypselae
Treatment appears in FNA Volume 21. Treatment on page 258. Mentioned on page 255.

Annuals, 4–62 cm. Stems erect, branched distally. Leaves mostly cauline; proximal opposite, distal alternate; ± sessile; blades linear, margins entire or toothed, faces hirsute or villous and (distal leaves) sparsely glandular-pubescent. Heads radiate, borne singly or in loose, ± corymbiform arrays. Peduncular bracts: pit-glands, tack-glands, and/or spines 0 at tips. Involucres ± campanulate to cylindric or ellipsoid, 3–12+ mm diam. Phyllaries 3–8 in 1 series (± lance-linear, herbaceous, each fully enveloping a ray ovary, abaxially hirsute or villous and sparsely glandular-pubescent or eglandular). Receptacles flat to convex (setulose), paleate (paleae falling, in 1 series between rays and disc, distinct). Ray florets 3–8, pistillate, fertile; corollas yellow, turning reddish (lobes ± parallel). Disc florets 4–35, bisexual and fertile; corollas yellow to reddish, tubes ± equaling narrowly funnelform throats, lobes 5, lance-deltate (anthers ± dark purple; styles glabrous proximal to branches). Ray cypselae (black) obcompressed, clavate (10-ribbed, straight, basal attachments centered, apices beakless, faces glabrous or ± scabrous); pappi 0. Disc cypselae (brown to black) similar to rays (± scabrous); pappi of 10 white, oblong scales (apices obtuse). x = 8.


w North America, nw Mexico.


Species 1.

Selected References


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