Apium (Celery and Marshwort) is a genus of about 20 species of flowering plants in the family Apiaceae, with a subcosmopolitan distribution in Europe, Asia, Africa, South America and Australia. They are medium to tall biennial or perennial plants growing wet ground (marshes and saltmarshes). They grow up to 1 m high and have pinnate to bipinnate leaves and small white flowers in compound umbels.
The genus is the type genus of the family Apiaceae and the order Apiales.
Apium species, including garden celery, are eaten by the larvae of some Lepidoptera species including Angle Shades, Common Swift, Hypercompe icasia, The Nutmeg, Setaceous Hebrew Character and Turnip Moth.