Upright annual herb. Stems 20-300 mm, sparsely hairy, herbaceous, sometime spongy, 0.5-5.0 mm wide. Leaves alternate, spreading, consistently twice-pinnate, 8.0-80.0 x 2.0-15.0 mm, base dilated, clasping (northern populations) to prominently sheathing around the stem (often in southern populations), sheath 0.5-4.0 mm long; lobes 3.0-6.0 x 0.5-2.5 mm, leathery, light green, sparsely hairy to densely hairy, apices acute, margins entire. Capitula heterogamous, disciform, solitary, terminal, pedunculate, peduncle hairy, 5.0-25.0 mm. Involucre hemispherical, 2.0-6.0 x 3.0-7.0 mm, 1-seriate, sometimes 2-seriate, bracts lanceolate, 2.0-6.0 x 1.0-2.0 mm, glabrous, green to purplish, opaque, apex and margins scarious, distinctly three veined, secondary venation obscure. Receptacle flat, epaleate; pedicels linear, 0.3-1.0 mm at anthesis, uniform, attaching to floret apically. Disciform florets female, ca. 1 to 14, sometimes absent in head, in single outer series, corolla absent, style 0.2-0.4 mm, ovary marginally winged, glabrous to sparsely hairy on inner face. Disc florets bisexual, ca. 30 to 45, corolla 0.9-1.3 mm long, yellow to whitish, oblong, tube draped basally over ovary apex, resin canals not present, limb slightly wider than tube, 4 lobed; lobes triangular, upright to spreading, dorsally tuberculate, not glandular, anthers 0.5-1.2 mm long (including apical appendages), ecaudate, apical appendages ovate, acute; style terete with thickened base; branches truncate, papillate apically-dorsally; ovary marginally ribbed. Cypselas heteromorphic; disciform cypselas ovoid, ca. 1.1 x 0.7 mm, marginally winged, wing width ½ of the ovary, base slightly cordate, inner face glabrous to sparsely hairy; disc cypselas ovoid, ca. 1.4 x 0.5 mm, marginally ribbed, glabrous.
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Annuals to c. 40 cm high. Stems glabrous or with occasional appressed to spreading hairs. Leaves to c. 6 cm long, 1-or 2-pinnatisect, or uppermost leaves sometimes entire, sparsely hairy or glabrous. Capitulum 6–8 mm diam.; peduncle 0.5–2 (–3) cm long, c. 0.3 mm wide (pressed specimens), hardly obconical at maturity, sparsely hirsute at anthesis, with hairs antrorse to spreading; involucral bracts numerous; outer bracts oblong-ovate or oblong, 2–3 mm long, rounded to truncate. Marginal florets up to c. 10, 1-seriate, with weakly developed corolla and pedicels c. 1 mm long, or absent. Disc florets bisexual, numerous, with pedicels much longer than wide; corolla c. 1 mm long; limb pale yellow. Achenes of marginal florets 1–1.5 mm long, broadly oblong, with inner face papillose; wings thin to slightly spongy, as broad as body. Achenes of disc florets c. 1–1.5 mm long, oblong, glabrous or inner face sparsely papillose.
Sparsely pilose annual, up to 300 mm tall, with densely leafy stems, at length glabrous. Leaves alternate, clasping at base, pinnatipartite, with lobes linear-subulate, rigid, pungent-mucronate, often hook-pointed. Flowerheads disciform, solitary, shortly pedunculate; outer female florets in 1 row, corolla absent; disc florets bisexual, yellow to white. Cypselas of female florets flattened and winged, hairy on body, of disc florets turbinate, glabrous; pappus absent.
Annual to 30 cm. Leaves alternate, sheathing at base, bi-or tripinnatisect. Flower heads disciform, solitary on slender, leafy peduncles, yellow to white.
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