Indian borage

A long-lived herbaceous plant 20–50 cm tall with a woody base; the four-angled succulent stems are finely hairy. Leaves are opposite, thick, crisp and succulent, ovate to rounded with scalloped margins, pale green on both surfaces and softly hairy; bruised leaves give a strong lemony scent and a pungent oregano-like, spicy taste. Flowers are small, 4-stamened and red-purple, borne in terminal spikes; fruits are small, round and brown. The whole plant is aromatic due to essential oil rich in carvacrol and the red colouring compound colein, and it tastes warm and pungent.

The species is thought to be native to tropical Africa, the Arabian Peninsula and India; the naturalist Georg Eberhard Rumphius recorded it on Ambon Island (Indonesia) in the 17th century, hence the epithet amboinicus. Today it is grown as a herb, medicine and ornamental throughout the tropics — Southeast Asia, South Asia, Europe (as a houseplant), the Caribbean and Latin America — under local names such as Cuban oregano, Mexican mint and broad leaf thyme. In Vietnam, húng chanh (also tần dày lá, rau thơm lùn) is common around home gardens; fresh leaves steamed with rock sugar or honey are a folk remedy for coughs and sore throats in children; leaves are also eaten raw with bún, phở and salads and added to braised fish for aroma. The leaf essential oil is rich in carvacrol with antibacterial activity.