Cyclospermum leptophyllum

Annual, taprooted, short-lived rosetted, 1−several-stemmed at base, branched throughout with forks forming at most canopy nodes, decumbent to erect, 5–60 cm tall; shoots with basal and cauline leaves, glabrous, with a faint, carrotlike smell. Stems: cylindric, to 3 mm diameter, smooth, green-striped with light green to yellowish green veins. Leaves: helically alternate, 3–4-pinnately compound or dissected, petiolate, without stipules; petiole sheathing stem node, to 40 mm long or 2–10 mm long , channeled above, rounded on lower side, with membranous wings of larger leaves 2–10 × 3.5 mm wide at base, on cauline leaves < 2 mm long; blade of basal and lower cauline leaves ovate in outline, 30–100 × 25–35 mm, typically with opposite primary and secondary lateral leaflets, ultimate segments channeled, 2–5 × 0.5–1 mm, entire; blade of upper cauline leaves 25–55 × 40–80 mm long, 3-dimensional, with ± linear segments diverging acutely from axis, ultimate segments channeled, 3–18 × 0.3–0.7 mm. Inflorescence: compound umbel, appearing opposite leaves, of 2−3 open umbellets, 6−25-flowered, typically < 25 mm long, umbellet several-flowered, lacking bracts, glabrous; involucre absent; primary rays subequal and divergent, 8−20 mm long; involucel absent; pedicel divergent and ascending, thin, 3−6.5 mm long, the central pedicels infrequent and much shorter . Flower: bisexual, radial, 0.8−1 mm across; sepals absent; petals 5, spreading but with tip curved inward, oblong in outline, 0.35−0.5 mm long, white or sometimes pinkish or purplish red at tip or margin, acute at tip, lacking midridge on upper surface; stamens 5, free, ± 0.3 mm long; filaments spreading, tapered to tip, < 0.2 mm long, whitish; anthers dorsifixed, dithecal, 0.15 mm long, light yellow becoming purplish red, longitudinally dehiscent; pollen pale yellow; pistil 1; ovary inferior, 2-lobed with a 2-lobed platform on top, oblong compressed side-to-side, 0.5−0.7 mm long and wide, strongly ribbed, ribs 10 but those next to fruit axis shorter, stylopodium greenish, 2-chambered, each chamber with 1 ovule; styles ca. 0.1 mm long. Fruit: schizocarp, of 2 dry, 1-seeded halves , mericarps semi-ovate and 5-ribbed on broad sides, elliptic to oblong in edge view, flattish or slightly concave on inner face on fruit axis, 1.8–2 × 1.5–2 mm, typically brownish purple, the ribs prominent, corky, subequal in width but lateral ones shorter in length. Late November−early July.

Cyclospermum leptophyllum native to South America; widely naturalized as a weed in tropical and temperate regions and is considered a noxious weed in many areas.