Apium L.
Stems prostrate or ascending or rarely erect. Leaves once or twice pinnatisect, often rather thick; the segments tripartite. Compound rays 3–6, each with an umbel of rather numerous small white flowers. Fruit c. 3 mm long; mericarps with 5 thick ribs. Small perennial with a thick rootstock. Sea Celery
Leaflets divided, primary segments 2–3 times as long as broad. Widespread. Coastal dunes and headlands. Fl. spring–autumn Apium prostratumfiliforme
Leaflets divided or entire, primary segments 6–15 times as long as broad. Near inland creeks and brackish water. Fl. spring–summer Apium prostratumprostratum