Common names: ambulia, Asian marshweed

Family: Scrophulariaceae

Could be confused with: Cabomba, Gratiola, Hottonia, Myriophyllum, Pogostemon, Proserpinaca. Ranunculus.

Native distribution: Tropical Asia, Australasia, Africa.

Species commonly cultivated:
Limnophila aquatica Roxb. (Asia)
L. aromatica (Lam.) Merr. (L. aromaticoides Yang & Yen) (Asia & Australia)
L. australis Wannan & J.T. Waterh. (Australia)
L. brownii Wannan (Australia)
L. heterophylla Benth. (Asia)
L. indica (L.) Druce (Asia & Australia)
L. sessiliflora (Vahl) Blume (Asia)

Adventive distribution: North America.

Weed status: Limnophila sessiliflora is an aquatic weed on the U.S. federal noxious weed list. It is established in Florida and Texas.

Habit: Submersed, emergent and amphibious stem plant.

Brief description: Annual or perennial, rooted. Stems ascending or creeping; adventitious roots produced from leaf nodes. Leaves caulescent, decussate or whorled, sessile or petiolate, distinctly heterophyllous between submersed and emersed forms; emersed leaf blade entire, ovate to lanceolate; submersed blades often highly pinnatisect; venation pinnate. Flowers solitary in leaf axils or in terminal or axillary spikes or leafy racemes, sessile or pedicellate; sepals 5, subequal; corolla tubular or funnel shaped, 2-lipped; adaxial lip entire or 2-lobed; abaxial lip 3-lobed; white, pink, purple or blue, sometimes with conspicuous spots. Dispersal by numerous seeds or by stem fragments.

Natural habitat: Rivers, lakes and swamps.

Additional comments: Limnophila contains 36 species, of which 13 are considered aquatic. Most species have an aromatic (‘turpentine’) odor when damaged. There is confusion concerning the identity of the species traded as L. aromatica and L. aromaticoides. Some authorities separate the two species based on the arrangement of submersed leaves (opposite or 3-whorled in L. aromatica; 3 to 10-whorled in L. aromaticoides). Recent consensus suggests that L. aromatica is simply a highly variable species in flower color and leaf arrangement and L. aromaticoides is one such variety. Limnophila aromatica, also know as Rau om or Rau ngo (in Vietnamese), is sold widely as a fresh herb to garnish and flavor soups & curries.