Cyclospermum leptophyllum (Pers.) Britt. & P. Wilson, marsh parsley. 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 ( Daucus) smell.

Stems

Stems cylindric, to 3 mm diameter, smooth, green–striped with light green to yellowish green veins.

Leaves

Leaves helically alternate, 3—4–pinnately compound or dissected, petiolate, without stipules; petiole sheathing stem node, to 40 mm long (basal and lower cauline leaves) or 2—10 mm long (upper cauline leaves), 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(—30) × 0.3—0.7 mm.

Inflorescence

Inflorescence compound umbel, appearing opposite leaves, of 2—3(—5) open umbellets, 6—25–flowered, typically < 25(—35) 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(—16) mm long, the central pedicels infrequent and much shorter (central flower subsessile).

Flower

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 (inner) 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 (stylopodium, stylar tissue) 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, 2–chambered, each chamber with 1 ovule, stylopodium greenish; styles 2, ca. 0.1 mm long.

Fruit

Fruit schizocarp, of 2 dry, 1–seeded halves (mericarps), 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, (1.3—)1.8—2(—3) × 1.5—2 mm, typically brownish purple, the ribs prominent, corky, subequal in width but lateral ones shorter in length.

A. C. Gibson & B. A. Prigge