Acmella oleracea aka Toothacheplant

Acmella oleracea is an herb with soft stems. It belongs to the aster family. People call it toothache plant, Pará cress, or buzz buttons. Its exact place of origin is still unclear. Kew lists it as a plant grown in southeastern Brazil. Other sources suggest it came from a wider South American area. It lives for years in warm places with no frost. Where winters freeze, gardeners often grow it for one year.

In gardens, plants reach about 1–1.6 feet (0.3–0.5 m) tall and wide. One botanical source records heights near 3 feet (0.9 m). The plant grows fast and forms a bushy, spreading shape. Its smooth stems may stand upright or lie along the ground. They can be green or tinged with red. The simple leaves grow in pairs, opposite each other. Their broad blades are egg-shaped or shaped like a triangle. They have toothed edges and pointed tips. The leaves are deep green, often with a bronze cast.

Small, round flower heads rise above the leaves. Each holds many tiny flowers called disc florets. They have no showy outer petals. The heads range from yellow to orange. Some have red centers. Each head measures less than an inch across. The flowers bloom from midsummer into early fall. Small black fruits called achenes form next. Bees and butterflies visit the plant. Sources also report visits from fireflies and birds. Gardeners use it in beds, borders, and pots. They also grow it in hanging baskets. The flower heads suit both fresh and dried displays.

Give this plant sun and rich soil that drains well. It also accepts part shade. Keep the soil moist. Sources list both acidic and neutral soil conditions. RHS rates it H2, so it cannot survive freezing. NC State lists USDA zones 9–11. Sow seeds where there is no frost. Leave them uncovered so they get light. Move young plants outside once the risk of frost has passed. You can also grow plants from softwood cuttings in summer. It needs no pruning. Sources report few problems with pests or disease.

People eat the leaves raw or cooked in salads and soups. Their sharp taste makes the mouth tingle and go numb. It also brings more saliva. People can eat small amounts of the flowers, with similar effects. People have long used it to ease toothache. They also use it to treat mouth or throat complaints. These uses do not prove that it works as medicine. Sources report no known hazards. They do not show that it is safe for pets. Extracts also have uses for killing insects. Plants can escape gardens and grow in wet sites. Useful Tropical Plants lists it as invasive in New Caledonia.