Slender celery
Cyclospermum leptophyllum (Apium leptophyllum)

Erect annual herb, 15–70 cm high, glabrous.
Leaves usually 2.5–4 cm long, 3–4 times dissected; segments filiform, to 1 mm wide, glabrous; lower leaves petiolate; upper leaves sessile.
Inflorescences with umbels 1.5–2.5 cm diameter; sessile or shortly pedunculate; rays 2–4, 8–16 mm long; umbellules 8–12 mm diameter; pedicels usually 6–20, 3–7 mm long. Flowers with petals c. 0.3 mm long, white.
Fruit ovoid, 1–3 mm long, glabrous.